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Physicists Twist Light, Send 'Hello World' Message Between Islands
Great find and THANKS for sharing to help teach all of us to keep looking in ANU way forward in TIME. Worship Par-ty

Bob... Ninja Alien2
"The Morning Light, No sensation to compare to this, suspended animation, state of bliss, I keep my eyes on the circling sky, tongue tied and twisted just and Earth Bound Martian I" Learning to Fly Pink Floyd [Video:]
Transfer of atomic mass with a photon solves the momentum paradox of light
by Staff Writers
Helsinki, Finland (SPX) Jul 07, 2017

[Image: optical-force-atoms-forms-mass-density-w...ght-lg.jpg]
The optical force on atoms forms a mass density wave that propagates with light through the crystal. Credit Jyrki Hokkanen / CSC - IT Center for Science

In a recent publication, Aalto University researchers show that in a transparent medium each photon is accompanied by an atomic mass density wave. The optical force of the photon sets the medium atoms in motion and makes them carry 92% of the total momentum of light, in the case of silicon.
The novel discovery solves the centennial momentum paradox of light. In the literature, there has existed two different values for the momentum of light in the transparent medium. Typically, these values differ by a factor of ten and this discrepancy is known as the momentum paradox of light. The difference between the momentum values is caused by neglecting the momentum of atoms moving with the light pulse.
To solve the momentum paradox the authors prove that the special theory of relativity requires an extra atomic density to travel with the photon. In related classical computer simulations, they use optical force field and Newton's second law to show that a wave of increased atomic mass density is propagating through the medium with the light pulse.
The mass transfer leads to splitting of the total momentum of light into two components. The fields' share of momentum is equal to the Abraham momentum while the total momentum, which includes also the momentum of atoms driven forward by the optical force, is equal to the Minkowski momentum.
"Since our work is theoretical and computational it must be still verified experimentally, before it can become a standard model of light in a transparent medium. Measuring the total momentum of a light pulse is not enough but one also has to measure the transferred atomic mass. This should be feasible using present interferometric and microscopic techniques and common photonic materials", researcher Mikko Partanen says.
Potential interstellar applications of the discovery
The researchers are working on potential optomechanical applications enabled by the optical shock wave of atoms predicted by the new theory. However, the theory applies not only to transparent liquids and solids but also to dilute interstellar gas.
Using a simple kinematic consideration it can be shown that the energy loss caused by the mass transfer effect becomes for dilute interstellar gas proportional to the photon energy and distance travelled by light.
"This prompts for further simulations with realistic parameters for interstellar gas density, plasma properties and temperature. Presently the Hubble's law is explained by Doppler shift being larger from distant stars.
"This effectively supports the hypothesis of expanding universe. In the mass polariton theory of light this hypothesis is not needed since redshift becomes automatically proportional to the distance from the star to the observer", explains Professor Jukka Tulkki.

Snell's Law

Snell's Law determines the angle at which a beam of light bends, according to the initial angle and the indexes of refraction of the two materials.

Light going from one material to another

If A is the index of refraction of the first material and a is the angle of the incoming ray or beam of light with respect to the perpendicular or normal to the surface, then b will be the angle to the normal of the ray in the second material where B is its index of refraction.


Light is bent going from first material to second

The Index of Refection for each material equals the speed of light in a vacuum (c) divided by the speed of light in the material. Thus

Quote:A = c/cA


Quote:B = c/cB

  • A is the index of refraction of material A

  • B is the index of refraction of material A
Since index B is greater than index A, the speed of light in material B is less than the speed in material A. Thus, according to Snell's Law, the angle b is less than the angle a.


Snell's Law is written as:

Quote:A*sin(a) = B*sin(b)

  • sin(a) is the sine of angle a

  • sin(b) is the sine of angle b
Calculating values

Typically, you want to find angle b or how much the light will be bend in the second material. Using some Algebra, Snell's Law can be rewritten as:

sin(b) = A*sin(a)/B


b = arcsin[A*sin(a)/B]

where arcsin[A*sin(a)/B] is the arcsine or angle whose sine is A*sin(a)/B.

Thus if the first material is air (index approximately = 1), the incoming angle is 30o and the second material is glass with an index = 1.5, you can calculate the angle of the light in glass.

Quote:sin(b) = A*sin(a)/B
sin(b) = 1*sin(30o)/ 1.5
sin(b) = 0.5/ 1.5 = 0.33
b = arcsin(0.33) = 19.5o
Thus, if light hits glass at 30o, its angle will change to 19.5o within the glass. Of course, if it is a glass plate, you will then use the opposite to obtain the exit angle of 30o back into air.
Along the vines of the Vineyard.
With a forked tongue the snake singsss...
(07-10-2017, 02:24 AM)Vianova  Said in another thread Wrote: ...#31

Less than 1 minute ago

Quote:A photon from standard light will typically scatter at the same angle and energy 
it featured before striking the electron, 
regardless of how bright its light might be. 

Yet Umstadter's team found that, above a certain threshold, 
the laser's brightness altered the angle, 
shape and wavelength 
of that scattered light.

The angle alteration is fascinating, and I wonder of the "angle alteration" is significant enough,
or just slight,
and if the angle is consistent above the threshold brightness.
It would be great to see the numeric data on the angle and wavelength differentials.
A fantastic discovery actually.

Vianova I am going to post this because it exactly is in the feedback loop.
The Magic Angle?
Then after That I am going to copy and paste this whole cloth response because I will paste it in another thread where it also belongs equally as a response.

Physicists Twist Light, Send 'Hello World' Message Between Islands (Pages: 1 2 )

So after I post this here it will end up there>>>#31

Less than 1 minute ago too.

Directing the path of light-induced electron transfer at a molecular fork using vibrational excitation[Image: ss-sing.jpg]

Nature Chemistry (2017) doi:10.1038/nchem.2793Received 06 October 2016 Accepted 05 May 2017 Published online 19 June 2017

Magic Angle: Where I photo-sync this eye's...

New research uncovers the secrets of photosynthesis that could help develop computer technology

July 11, 2017 by Kirsty Bowen

[Image: 2-newresearchu.jpg]
Illustrating how the destination of an electron (represented by the train) can be directed following application of an ultra-fast mid-infrared pulse (represented by the fire). Credit: Helen Towrie at the CLF
Scientists at the University of Sheffield have published new research illuminating how energy is transferred in molecules - something that could influence new molecular technologies for the future.

Energy and charge transfer is what drives photosynthesis and any solar-to-chemical or electrical-to-chemical energy conversion.
Working with collaborators at the Science and Technology Facilities Council (STFC) Central Laser Facility (CLF), Professor Julia Weinstein and Dr Anthony Meijer studied a new 'fork' molecule that can direct the destination of an electron in a precise manner when a particular infrared light pulse is applied.
The key finding of the work, published in Nature Chemistry, is that scientists can direct energy transfer via light at a molecular level.
Professor Weinstein said: "Previous research has enabled us to switch electron transfer on or off. What makes our research so exciting is that, via our synthetic molecule, we can now direct the path of an electron in a very specific and controlled way."
Electron transfer is an important part of many natural processes, including the light harvesting process by which plants create and store energy through photosynthesis.
Professor Weinstein explains: "In creating this 'molecular fork', we now have the ability to model natural molecular processes, such as photosynthesis. If we can replicate how energy is stored and utilised, then we have the basis to develop exciting new molecular technologies for the future.
"From new ways of capturing and storing the energy coming to us from the Sun, to developing new forms of computing technology, this research opens up some exciting new opportunities."
The ability to direct charge along one of several pathways can be used for information storage and retrieval in computing, using low-energy red light.
[Image: 1x1.gif] Explore further: Energy jumps back and forth between molecules during transfers
More information: Milan Delor et al. Directing the path of light-induced electron transfer at a molecular fork using vibrational excitation, Nature Chemistry (2017). DOI: 10.1038/nchem.2793 

Read more at:

No mention of the Magic Angle there?  

Magic Angle:

The angle alteration is fascinating, and I wonder of the "angle alteration" is significant enough,

or just slight,
and if the angle is consistent above the threshold brightness.
It would be great to see the numeric data on the angle and wavelength differentials.
A fantastic discovery actually.

Read on>>> Magic Angle...

Directing the path of light-induced electron transfer at a molecular fork using vibrational excitation

Nature Chemistry (2017) doi:10.1038/nchem.2793Received 06 October 2016 Accepted 05 May 2017 Published online 19 June 2017

Ultrafast electron transfer in condensed-phase molecular systems is often strongly coupled to intramolecular vibrations that can promote, suppress and direct electronic processes. Recent experiments exploring this phenomenon proved that light-induced electron transfer can be strongly modulated by vibrational excitation, suggesting a new avenue for active control over molecular function. Here, we achieve the first example of such explicit vibrational control through judicious design of a Pt(II)-acetylide charge-transfer donor–bridge–acceptor–bridge–donor ‘fork’ system: asymmetric 13C isotopic labelling of one of the two –C≡C– bridges makes the two parallel and otherwise identical donor→acceptor electron-transfer pathways structurally distinct, enabling independent vibrational perturbation of either. Applying an ultrafast UVpump(excitation)–IRpump(perturbation)–IRprobe(monitoring) pulse sequence, we show that the pathway that is vibrationally perturbed during UV-induced electron transfer is dramatically slowed down compared to its unperturbed counterpart. One can thus choose the dominant electron transfer pathway. The findings deliver a new opportunity for precise perturbative control of electronic energy propagation in molecular devices.  Nature Chemistry (2017). DOI: 10.1038/nchem.2793 

No mention of the Magic Angle there?  

Magic Angle: Two Quotes hidden in the supplementary PDF.

 UV and IR pumps were in parallel polarization to each other, while the probe beam was set at magic angle with respect to these pumps. 

 The pump energy at the sample was 0.8 μJ and the relative polarisation was set to magic angle.

Allow wiki to define the Magic Angle:

The magic angle θm is

{\displaystyle \theta _{\mathrm {m} }=\arccos {\frac {1}{\sqrt {3}}}=\arctan {\sqrt {2}}\approx 0.955\,32\ {\text{rad}}\approx 54.7^{\circ }\!,}[Image: dfa9685d06f5c2f94fd0471a4742a7874568d31d]

[Image: Magic_angle.png]

where arccos and arctan are the inverse cosine and tangent functions respectively.[Image: 11px-OEISicon_light.svg.png]A195696
θm is the angle between the space diagonal of a cube and any of its three connecting edges, see image.
Magic angle θ is also half of the opening angle formed when a cube is rotated from its space diagonal axis, which may be represented as arccos −1/3 or 2 arctan √2 radians ≈ 109.4712°. This double magic angle is directly related to Tetrahedral molecular geometry and is the angle from one vertex to the exact center of the tetrahedron (i.e., the edge central angle also known as the tetrahedral angle).

[Image: nchem.2793-f1.jpg]  [Image: nchem.2793-f2.jpg]  [Image: nchem.2793-f3.jpg]  [Image: nchem.2793-f4.jpg]

Magic Angle?
Along the vines of the Vineyard.
With a forked tongue the snake singsss...
Quote:"It's not a hologram, it's really three-dimensionally structured light."  Holycowsmile 

Better than Star Wars: Chemistry discovery yields 3-D table-top objects crafted from light
July 11, 2017 by Margaret Allen

[Image: betterthanst.jpg]
The set-up for the SMU 3-D light pad includes this ultraviolet projector as well as a visible projector. The two project patterns of light into a chamber of photoactivatable dye. Wherever the UV light intersects with the green light it generates a 3-dimensional image inside the chamber. Credit: SMU
A scientist's dream of 3-D projections like those he saw years ago in a Star Wars movie has led to new technology for making animated 3-D table-top objects by structuring light.

The new technology uses photoswitch molecules to bring to life 3-D light structures that are viewable from 360 degrees, says chemist Alexander Lippert, Southern Methodist University, Dallas, who led the research.
The economical method for shaping light into an infinite number of volumetric objects would be useful in a variety of fields, from biomedical imaging, education and engineering, to TV, movies, video games and more.
"Our idea was to use chemistry and special photoswitch molecules to make a 3-D display that delivers a 360-degree view," Lippert said. "It's not a hologram, it's really three-dimensionally structured light."
Key to the technology is a molecule that switches between non-fluorescent and fluorescent in reaction to the presence or absence of ultraviolet light.
The new technology is not a hologram, and differs from 3-D movies or 3-D computer design. Those are flat displays that use binocular disparity or linear perspective to make objects appear three-dimensional when in fact they only have height and width and lack a true volume profile.
"When you see a 3-D movie, for example, it's tricking your brain to see 3-D by presenting two different images to each eye," Lippert said. "Our display is not tricking your brain—we've used chemistry to structure light in three actual dimensions, so no tricks, just a real three-dimensional light structure. We call it a 3-D digital light photoactivatable dye display, or 3-D Light Pad for short, and it's much more like what we see in real life."
At the heart of the SMU 3-D Light Pad technology is a "photoswitch" molecule, which can switch from colorless to fluorescent when shined with a beam of ultraviolet light.
The researchers discovered a chemical innovation for tuning the photoswitch molecule's rate of thermal fading—its on-off switch—by adding to it the chemical amine base triethylamine.
Now the sky is the limit for the new SMU 3-D Light Pad technology, given the many possible uses, said Lippert, an expert in fluorescence and chemiluminescence—using chemistry to explore the interaction between light and matter.

For example, conference calls could feel more like face-to-face meetings with volumetric 3-D images projected onto chairs. Construction and manufacturing projects could benefit from rendering them first in 3-D to observe and discuss real-time spatial information. For the military, uses could include tactical 3-D replications of battlefields on land, in the air, under water or even in space.
Volumetric 3-D could also benefit the medical field.
"With real 3-D results of an MRI, radiologists could more readily recognize abnormalities such as cancer," Lippert said. "I think it would have a significant impact on human health because an actual 3-D image can deliver more information."
Unlike 3-D printing, volumetric 3-D structured light is easily animated and altered to accommodate a change in design. Also, multiple people can simultaneously view various sides of volumetric display, conceivably making amusement parks, advertising, 3-D movies and 3-D games more lifelike, visually compelling and entertaining.
Lippert and his team report on the new technology and the discovery that made it possible in the article "A volumetric three-dimensional digital light photoactivatable dye display," published in the journal Nature Communications.
Co-authors are Shreya K. Patel, lead author, and Jian Cao, both students in the SMU Department of Chemistry.
Genesis of an idea—cinematic inspiration
The idea to shape light into volumetric animated 3-D objects came from Lippert's childhood fascination with the movie "Star Wars." Specifically he was inspired when R2-D2 projects a hologram of Princess Leia. Lippert's interest continued with the holodeck in "Star Trek: The Next Generation."

From watching Star Wars as a child, SMU chemist Dr. Alex Lippert brought to life his dream of crafting animated 3-D shapes from light.Using photoswitch chemistry his lab constructed light shapes into structures that have volume and are viewable from 360 degrees, making them useful for biomedical imaging, teaching, engineering, TV, movies, video games and more. Credit: (SMU)
"As a kid I kept trying to think of a way to invent this," Lippert said. "Then once I got a background in chemistry molecules that interact with light, and an understanding of photoswitches, it finally dawned on me that I could take two beams of light and use chemistry to manipulate the emission of light."
Key to the new technology was discovering how to turn the chemical photoswitch off and on instantly, and generating light emissions from the intersection of two different light beams in a solution of the photoactivatable dye, he said.
SMU graduate student in chemistry Jian Cao hypothesized the activated photoswitch would turn off quickly by adding the base. He was right.
"The chemical innovation was our discovery that by adding one drop of triethylamine, we could tune the rate of thermal fading so that it instantly goes from a pink solution to a clear solution," Lippert said. "Without a base, the activation with UV light takes minutes to hours to fade back and turn off, which is a problem if you're trying to make an image. We wanted the rate of reaction with UV light to be very fast, making it switch on. We also wanted the off-rate to be very fast so the image doesn't bleed."
SMU 3-D Light Pad
In choosing among various photoswitch dyes, the researchers settled on N-phenyl spirolactam rhodamines. That particular class of rhodamine dyes was first described in the late 1970s and made use of by Stanford University's Nobel prize-winning W.E. Moerner.
The dye absorbs light within the visible region, making it appropriate to fluoresce light. Shining it with UV radiation, specifically, triggers a photochemical reaction and forces it to open up and become fluorescent.
Turning off the UV light beam shuts down fluorescence, diminishes light scattering, and makes the reaction reversible—ideal for creating an animated 3-D image that turns on and off.
"Adding triethylamine to switch it off and on quickly was a key chemical discovery that we made," Lippert said.
To produce a viewable image they still needed a setup to structure the light.
Structuring light in a table-top display
The researchers started with a custom-built, table-top, quartz glass imaging chamber 50 millimeters by 50 millimeters by 50 millimeters to house the photoswitch and to capture light.
Inside they deployed a liquid solvent, dichloromethane, as the matrix in which to dissolve the N-phenyl spirolactam rhodamine, the solid, white crystalline photoswitch dye.
Next they projected patterns into the chamber to structure light in two dimensions. They used an off-the-shelf Digital Light Processing (DLP) projector purchased at Best Buy for beaming visible light.
The DLP projector, which reflects visible light via an array of microscopically tiny mirrors on a semiconductor chip, projected a beam of green light in the shape of a square. For UV light, the researchers shined a series of UV light bars from a specially made 385-nanometer Light-Emitting Diode projector from the opposite side.
Where the light intersected and mixed in the chamber, there was displayed a pattern of two-dimensional squares stacked across the chamber. Optimized filter sets eliminated blue background light and allowed only red light to pass.
To get a static 3-D image, they patterned the light in both directions, with a triangle from the UV and a green triangle from the visible, yielding a pyramid at the intersection, Lippert said.
From there, one of the first animated 3-D images the researchers created was the SMU mascot, Peruna, a racing mustang.
[Image: 1-betterthanst.jpg]
SMU chemist Dr. Alex Lippert and his lab developed the SMU 3-D light pad (shown here). It includes an ultraviolet projector and a visible projector, which project patterns of light into a chamber of photoactivatable dye. Wherever the UV light intersects with the green light it generates a 3-dimensional image inside the chamber. Credit: SMU
"For Peruna—real-time 3-D animation—SMU undergraduate student Shreya Patel found a way to beam a UV light bar and keep it steady, then project with the green light a movie of the mustang running," Lippert said.
So long Renaissance
Today's 3-D images date to the Italian Renaissance and its leading architect and engineer.
"Brunelleschi during his work on the Baptistery of St. John was the first to use the mathematical representation of linear perspective that we now call 3-D. This is how artists used visual tricks to make a 2-D picture look 3-D," Lippert said. "Parallel lines converge at a vanishing point and give a strong sense of 3-D. It's a useful trick but it's striking we're still using a 500-year-old technique to display 3-D information."
The SMU 3-D Light Pad technology, patented in 2016, has a number of advantages over contemporary attempts by others to create a volumetric display but that haven't emerged as commercially viable.
Some of those have been bulky or difficult to align, while others use expensive rare earth metals, or rely on high-powered lasers that are both expensive and somewhat dangerous.
The SMU 3-D Light Pad uses lower light powers, which are not only cheaper but safer. The matrix for the display is also economical, and there are no moving parts to fabricate, maintain or break down.
Lippert and his team fabricated the SMU 3-D Light Pad for under $5,000 through a grant from the SMU University Research Council.
"For a really modest investment we've done something that can compete with more expensive $100,000 systems," Lippert said. "We think we can optimize this and get it down to a couple thousand dollars or even lower."
Next Gen: SMU 3-D Light Pad 2.0
The resolution quality of a 2-D digital photograph is stated in pixels. The more pixels, the sharper and higher-quality the image. Similarly, 3-D objects are measured in voxels—a pixel but with volume. The current 3-D Light Pad can generate more than 183,000 voxels, and simply scaling the volume size should increase the number of voxels into the millions—equal to the number of mirrors in the DLP micromirror arrays.
For their display, the SMU researchers wanted the highest resolution possible, measured in terms of the minimum spacing between any two of the bars. They achieved 200 microns, which compares favorably to 100 microns for a standard TV display or 200 microns for a projector.
The goal now is to move away from a liquid vat of solvent for the display to a solid cube table display. Optical polymer, for example, would weigh about the same as a TV set. Lippert also toys with the idea of an aerosol display.
The researchers hope to expand from a monochrome red image to true color, based on mixing red, green and blue light. They are working to optimize the optics, graphics engine, lenses, projector technology and photoswitch molecules.
"I think it's a very fascinating area. Everything we see—all the color we see—arises from the interaction of light with matter," Lippert said. "The molecules in an object are absorbing a wavelength of light and we see all the rest that's reflected. So when we see blue, it's because the object is absorbing all the red light. What's more, it is actually photoswitch molecules in our eyes that start the process of translating different wavelengths of light into the conscious experience of color. That's the fundamental chemistry and it builds our entire visual world. Being immersed in chemistry every day—that's the filter I'm seeing everything through."
The SMU discovery and new technology, Lippert said, speak to the power of encouraging young children.
"They're not going to solve all the world's problems when they're seven years old," he said. "But ideas get seeded and if they get nurtured as children grow up they can achieve things we never thought possible."
[Image: 1x1.gif] Explore further: Researchers use laser-generated bubbles to create 3-D images in liquid
More information: Shreya K. Patel et al, A volumetric three-dimensional digital light photoactivatable dye display, Nature Communications (2017). DOI: 10.1038/ncomms15239 
Journal reference: Nature Communications [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: Southern Methodist University

Read more at:
Along the vines of the Vineyard.
With a forked tongue the snake singsss...
(06-27-2017, 01:23 AM)rhw007 Wrote: Great find and THANKS for sharing to help teach all of us to keep looking in ANU way forward in TIME. Worship Par-ty

Bob... Ninja Alien2

Quantum Quirk: Experiment Proves What Happens in the Future Affects the Past
  • Jun 21, 2017

  • 0


Running light around a tetrahedron
July 17, 2017

[Image: runninglight.png]
The moment of truth in the initial test phase - first light, scattered off a mirror. Each of the four rings forms a triangle, around which counter-propagating laser beams are directed by mirrors at each corner. Credit: Geophysical Observatory
Thanks to an innovative ring laser design, geophysicists at LMU can now measure and monitor Earth's rotation with unprecedented accuracy. The new instrument in Fürstenfeldbruck will be formally inaugurated this week.

The world has so far taken relatively little notice of Fürstenfeldbruck, a town located about 20 km from Munich. It certainly doesn't rate as a hotspot for cutting-edge science. But that is about to change. For geophysicists based at LMU and the Technical University of Munich (TUM) have built an instrument there which sets a new standard in its field. Buried in an underground bunker built amid cropland and open fields, the device takes up several hundred cubic meters of space. Its purpose is to measure rotational ground motions with greater sensitivity and precision than any other machine in existence.
Even the editors of the leading research journal Science are clearly impressed by the dimensions – and the capabilities – of the new instrument. In a news feature that appeared in a recent issue of the magazine, the novel ring laser is referred to as the "most sophisticated" instrument of its kind in the world. The leader of the ROMY (Rotational Motions in Seismology) project is Heiner Igel, Professor of Seismology at LMU. The concept won him one of the richly endowed Advanced Investigator Grants awarded by the European Research Council (ERC), and the LMU went on to supply the additional funding required for its final realization. The initial tests and experiments have been successful, and the instrument will be officially put into service this week.
Our restless planet
Ring lasers are exquisitely sensitive to rotational motion. They can, for example, measure the Earth's rotation with extremely high precision. Our planet is never at rest, rotating on its own axis every day and orbiting the Sun once a year. But it doesn't follow exactly the same course year for year. Its trajectory is subject to minimal deviations. In fact, it behaves just like a child's spinning top: Neither the orientation of its axis nor the speed of its rotation is constant. It is buffeted by strong winds in the upper atmosphere and by ocean currents at depth, and massive earthquakes knock it out of kilter. But then, the Earth itself is anything but a perfect sphere. No wonder it fails to follow the ideal of perfect circular motion that Aristotle once prescribed for it.

Credit: Ludwig Maximilian University of Munich
Moreover, quantifying the minimal variations in the many different components of the Earth's motions is not solely a matter of academic interest. For example, all GPS-based navigational systems must be periodically recalibrated in order to take account of these variations, which would otherwise give rise to significant errors in determining one's position on the globe. This task is currently done with the aid of Very Long Baseline Interferometry (VLBI), which uses a network of radio telescopes to determine the distances between the Earth and selected quasars in deep space that are millions of light-years from us. But this method is complicated and it takes days to arrive at the final result. The Munich researchers believe that their new ring laser will enable them to achieve at least the same accuracy in far less time. If they are right, results could be updated within seconds rather than days.

But this is only a small part of Heiner Igel's vision for the new high-end instrument. – He intends to open up a whole new dimension in seismology by using it to carry out more detailed analyses of seismically induced ground motions. For when an earthquake occurs, the ground not only shakes up and down, and back and forth. Tremors are also characterized by tilting and rotational motions around a fixed point. So far, seismologists have had to ignore such motions, simply because conventional seismometers provide no means of measuring them. However, Igel believes – contrary to received wisdom – that a realistic and complete picture of ground motions during earthquakes requires the acquisition and integration of this information.
Indeed, he and his colleagues hope that the new ring laser will provide answers to a whole series of open questions. For instance, rotation sensors can measure the magnitude of tilting and rotational ground motions, which structural engineers need to enhance the stability of buildings in earthquake zones. Rotation sensors can also provide data that give insights into anomalous magma dynamics in active volcanoes, and thus serve to improve the quality of corresponding modeling studies. In combination with other methods, such measurements permit geophysicists to probe the properties and the dynamics of the Earth's interior, Igel explains. And that's not all. ROMY also promises to shed new light on how the world's oceans interact physically with the planet, causing it to oscillate permanently.
The principle on which the instrument's operation is based was first demonstrated by the French physicist Georges Sagnac shortly before the outbreak of the First World War: He showed a beam of light is directed around a closed course (with the aid of mirrors), the time it takes to complete a circuit is independent of the direction in which it propagates. However, if the apparatus is rotated, the beam travelling in the same sense as the rotation takes slightly longer for each lap – because it has to cover a greater distance than a beam transmitted in the opposite direction. Due to this difference in path-length, two counter-propagating beams will be phase shifted with respect to one another and, when recombined, they produce a typical interference pattern. In exactly the same way, when two notes that are slightly out of tune are sounded together, they produce a characteristic beat note which varies regularly in pitch. Moreover, the rotation rate can be calculated from the frequency of the beat note produced when the counter-propagating beams are superimposed.
Igel and laser physicist Ulrich Schreiber from the TUM made use of this principle in their design for ROMY to measure spin or tilting motions. In this case, the laser beams are propagated along not one but four axes. Each of the four light paths forms the edges of an equilateral triangle with sides 12 m long, At each apex, the light is deflected by mirrors, whose positions can be adjusted with high precision. Together, the four rings form the faces of a regular, inverted tetrahedron whose apex lies 15 m underground. This set-up enables the scientists to measure rotational motions in all directions.
[Image: 1-runninglight.png]
A view of the ring laser in the course of construction. Credit: Geophysical Observatory
Five km of optic fiber, tightly wound
"It took us two years to work out how to build it," Igel says. To ensure high sensitivity, the ring lasers must be shielded from environmental interference. For example, in order to protect the instrument from ground water, it was enclosed in a tetrahedral concrete shell – like a plant in a flower pot. Igel realized early on that he needed to have his colleague from the TUM onboard to make the project a success – for Schreiber had already designed and built several ring-laser systems in Germany, New Zealand, the USA, Italy and elsewhere. ROMY, however, is undoubtedly his masterpiece. Incorporating computer-controlled precision engineering into an instrument with dimensions of 12 m requires a new level of meticulousness.
Meanwhile, the instrument has not only been tested and calibrated, it has already performed a whole series of measurements which will form the basis for several publications. For example, some of the aftershocks observed after the series of earthquakes in Norcia in Central Italy in October 2016 have been characterized, as well as the seismic noise generated by the Earth's oceans.
Recording the hitherto unquantifiable tilt and rotational motions in the field, i.e. in the vicinity of the seismic focus of an earthquake, will require the use of portable instruments, Igel says – and the researchers responsible for ROMY have already taken a major step towards this goal. They have teamed up with a specialist company in France to develop a portable fibre-optic-based sensor, and the first prototypes were on show at a large geosciences conference held in Vienna in April. These instruments use an extremely thin optic fiber of 5 km in length, which is coiled onto a spool: "A real milestone," Igel enthuses. The initial measurements performed in Central Italy, and on the volcanic island of Stromboli off the north coast of Sicily "look good," he says.
The pioneers in Munich hope that others will follow the example set by ROMY. If so, we should someday have a global network of ring-laser seismometers which can finally provide us with a truly comprehensive picture of the dynamics of the Earth's motions. In such a network, Fürstenfeldbruck's ring would serve as an essential node – a hotspot, so to speak.
[Image: 1x1.gif] Explore further: 'Going deep' to measure Earth's rotational effects
Journal reference: Science [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: Ludwig Maximilian University of Munich

Read more at:[url=][/url]
Along the vines of the Vineyard.
With a forked tongue the snake singsss...
Lately I've had recurring thoughts
about how the difference between
the speed of light in a vacuum
and the speed of light in a practical length* of fiber optics
can be measured.

* a classroom AFAIK
Laser beams for superconductivity: Research sheds light on unexpected physical phenomena
October 25, 2017

[Image: 1-laser.jpg]
Credit: ORNL
A laser pulse, a special material, an extraordinary property which appears inexplicably. These are the main elements that emerge from a research conducted by an international team, coordinated by Michele Fabrizio and comprising Andrea Nava and Erio Tosatti from SISSA, Claudio Giannetti from the Università Cattolica di Brescia and Antoine Georges from the Collège de France. The results of their study have recently been published in the journal Nature Physics. The key element of the study is a compound of the most symmetrical molecule that exists in Nature, namely C60 bucky-ball, a spherical fullerene.

Read more at:

New type of light interaction with atoms allows for manipulating cloud shape

October 24, 2017 by Bob Yirka report

[Image: newtypeoflig.jpg]
Credit: Physical Review Letters (2017). DOI: 10.1103/PhysRevLett.119.163201
A team of researchers at the Weizmann Institute of Science in Israel has found a new way to manipulate atoms using light. In their paper published in Physical Review Letters, the team describes the new technique and possible uses for it.

Read more at:
Along the vines of the Vineyard.
With a forked tongue the snake singsss...
'Twisted' light could illuminate new path for wireless communications
October 26, 2017

[Image: twistedlight.jpg]
Credit: University of Glasgow
Scientists have taken an important step towards using 'twisted' light as a form of wireless, high-capacity data transmission which could make fibre-optics obsolete.

In a new report published today (Thursday 26 October) in the journal Science Advances, a team of physicists based in the UK, Germany, New Zealand and Canada describe how new research into 'optical angular momentum' (OAM) could overcome current difficulties with using twisted light across open spaces.
Scientists can 'twist' photons – individual particles of light – by passing them through a special type of hologram, similar to that on a credit card, giving the photons a twist known as optical angular momentum.
While conventional digital communications use photons as ones and zeroes to carry information, the number of intertwined twists in the photons allows them to carry additional data – something akin to adding letters alongside the ones and zeroes. The ability of twisted photons to carry additional information means that optical angular momentum has the potential to create much higher-bandwidth communications technology.
While optical angular momentum techniques have already been used to transmit data across cables, transmitting twisted light across open spaces has been significantly more challenging for scientists to date. Even simple changes in atmospheric pressures across open spaces can scatter light beams and cause the spin information to be lost.
The researchers examined the effects on both the phase and intensity of OAM carrying light over a real link in an urban environment to assess the viability of these modes of quantum information transfer.
Their free space link, in Erlangen, Germany, was 1.6km in length and passed over fields and streets and close to high-rise buildings to accurately simulate an urban environment and atmospheric turbulence that can disrupt information transfer in space – a thorough approach that will be instrumental in moving OAM research forward.
Conducting this field tests in a real urban environment, has revealed exciting new challenges that will that must be overcome before systems can be made commercially available. Previous studies had indicated the potential feasibly of OAM communication systems, but had not fully characterised the effects of turbulent air on the phase of the structured light propagating over links of this length.

Dr. Martin Lavery, head of the Structured Photonics Research Group at University of Glasgow, is the lead author on the team's research paper. Dr Lavery said: "In an age where our global data consumption is growing at an exponential rate, there is mounting pressure to discover new methods of information carrying that can keep up with the huge uptake in data across the world.
"A complete, working optical angular momentum communications system capable of transmitting data wirelessly across free space has the potential to transform online access for developing countries, defence systems and cities around the world.
"Free space optics is a solution that can potentially give us the bandwidth of fibre, but without the requirement for physical cabling.
"This study takes vital steps forward in the journey towards high dimensional free space optics that can be a cheaper, more accessible alternative to buried fibre optics connections."
The turbulent atmosphere used in this experiment highlighted the fragility of shaped phase fronts, particularly for those that would be integral to high-bandwidth data transfers. This study indicated the challenges future adaptive optical systems will be required to resolve.
Dr. Lavery added: "With these new developments, we are confident that we can now re-think our approaches to channel modelling and the requirement places on adaptive optics systems. We are getting ever closer to developing OAM communications that can be deployed in a real urban setting.
"We want to start a conversation about the issues that need to be addressed and how we are going to move towards the resolution."
Dr Lavery undertook the work in partnership with researchers from the Max Planck Institute for the Science of Light and Institute of Optics, and the Universities of Otago, Ottawa and Rochester.
These findings allow researchers to address challenges – not previously observed – in developing adaptive optics for quantum information transfer to move closer towards a new age of free space optics that will eventually replace fibre optics as a functional mode of communication in urban environments and remote sensing systems.
The paper, titled "Free-space propagation of high dimensional structured optical fields in an urban environment," is published in Science Advances.
[Image: 1x1.gif] Explore further: Researchers demonstrate quantum teleportation of patterns of light
More information: Martin P. J. Lavery et al. Free-space propagation of high-dimensional structured optical fields in an urban environment, Science Advances (2017). DOI: 10.1126/sciadv.1700552 
Journal reference: Science Advances [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: University of Glasgow

Read more at:[/url][url=]
Along the vines of the Vineyard.
With a forked tongue the snake singsss...
Nanoscale 'abacus' uses pulses of light instead of wooden beads to perform calculations
November 2, 2017
[Image: abacus.jpg]
The quest to develop ever-faster and more powerful computers has led to one of the most rudimentary methods of counting being given a 21st century make-over.

An international team of researchers, including Professor C. David Wright from the University of Exeter, have developed a nanoscale optical 'abacus' - which uses light signals to perform arithmetic computations.
The innovative device works by counting pulses of light - much in the same way beads are used to count when using a conventional abacus - before storing the data.
This pioneering new technique could pave the way to new, more powerful computers that combine computing and storage functions in one element - a move away from conventional computers that treat these two functions as separate.
The study is published in leading scientific journal, Nature Communications.
Prof. C David Wright, an expert in electronic engineering and co-author of the study said: "This device is able carry out all the basic functions you'd associate with the traditional abacus - addition, subtraction, multiplication and division - what's more it can do this using picosecond (one-thousandth of a billionth of a second) light pulses".
Lead author of the study, Professor Wolfram Pernice from the Institute of Physics at Münster University in Germany added: "In the article we describe for the first time the realization of an abacus which operates in a purely optical way. Rather than wooden beads as found on traditional abacuses, our innovative device calculates with pulses of light - and simultaneously stores the result."
The team's optical abacus, which is so small it's essentially invisible to the naked eye, is installed on a photonic microchip that can be easily manufactured.
So far, the researchers have succeeded in calculating with two-digit numbers using two photonic phase-change cells, but the extension to large multi-digit numbers simply involves the use of more cells.
"Computing with light - and not with electrons, as is the case with traditional computers - means that we can develop much faster systems which can be connected using integrated optical waveguides." adds co-author Prof. Harish Bhaskaran from the University of Oxford.
[Image: 1x1.gif] Explore further: Move towards 'holy grail' of computing by creation of brain-like photonic microchips
More information: J. Feldmann et al, Calculating with light using a chip-scale all-optical abacus, Nature Communications (2017). DOI: 10.1038/s41467-017-01506-3 
Journal reference: Nature Communications [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: University of Exeter

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Optoelectronics without glass

November 3, 2017 by Fabio Bergamin

[Image: optoelectron.jpg]
Microscopic image of a chip. Top left: functional modulator with electrical contacts; right: test modulator without electrical contact; below: test components. Credit: ETH Zurich
Researchers at ETH Zurich have developed the first opto-electronic circuit component that works without glass and is instead made of metal. The component, referred to as a modulator, converts electrical data signals into optical signals. It is smaller and faster than current modulators, and much easier and cheaper to make.

Optical components for microelectronics must be made of glass. Metals are not suitable for this purpose, since optical data can propagate only across roughly a distance of 100 micrometres. This was the general view of scientists until recently. A team of researchers headed by Juerg Leuthold, professor in the Department of Information Technology and Electrical Engineering, has now succeeded in doing what was thought to be impossible and developed a light-processing component made of metal. The researchers have presented their findings in the latest issue of the journal Science.
They accomplished this feat by building a small enough component: at just 3 x 36 micrometres, it is within a size range in which both optical and electrical information can propagate in metals.
Component for fibre optic networks
The component is a modulator: modulators convert electrical data signals into optical signals. They are installed in modern internet routers used for fibre optic networks and enable fibre optic data connections between computer units in data centres. However, the standard components used today function differently than the new modulators.
The new component works by aiming the light from a fibre optic source at the modulator, causing the electrons on its surface to oscillate. Experts refer to this as a surface plasmon oscillation. This oscillation can be changed indirectly by electrical data pulses. When the oscillation of the electrons is converted back into light, the electrical information is now encoded onto the optical signal. This means that the information is converted from an electrical into an optical data pulse that can be transmitted via fibre optics.
[Image: 1-optoelectron.jpg]
Schematic representation of the metallic modulator: Left: a continuous beam of light strikes a metallic lattice that deflects the light onto the chip. Right: an optical data pulse exits the component. Credit: ETH Zurich
Faster and smaller
Two years ago, Leuthold and his colleagues developed one of these plasmonic modulators. At the time, it was the smallest and fastest modulator ever built, but the semiconductor chip still had various glass components.
By replacing all the glass components with metallic ones, the scientists have succeeded in building an even smaller modulator that works up to highest speed. "In metals, electrons can move at practically any speed, whereas the speed in glass is limited due to its physical properties," says Masafumi Ayata, a doctoral student in Leuthold's group and lead author of the study. In the experiment, the researchers succeeded in transmitting data at 116 gigabits per second. They are convinced that with further improvements, even higher data transfer rates will be possible.

Etched from a gold layer
The modulator prototype tested by the ETH researchers is made of a gold layer that lies on a glass surface. The scientists emphasised that the glass has no function. "Instead of the glass layer, we could also use other suitable smooth surfaces," says Leuthold. It might also be possible to use less expensive copper instead of gold for industrial applications. The important point is that only one metallic coating is required for the new modulators. "This makes them much easier and cheaper to fabricate," says Leuthold.
The researchers are already working with an industrial partner in order to put the new modulator into practice, and talks with other partners are in progress. However, Leuthold believes that further development may be required before the technology is ready for the market; for example, he expects that the current loss of signal strength during modulation can be reduced further.
For computers and autonomous vehicles
The new modulator could one day be used not only for telecommunications applications, but for computers as well. "The computer industry is considering using fibre optics to transfer data between the individual chips inside computers," says Leuthold. However, this would require tiny modulators – such as Leuthold and his team have developed.
Ultimately, it is also conceivable that the modulators could be used in displays – including bendable ones – and optical sensors, such as those in the Lidar system for distance measurement that are used in (semi-) autonomous cars.
[Image: 1x1.gif] Explore further: Smaller, faster, cheaper: A new type of modulator for the future of data transmission
More information: Masafumi Ayata et al. High-speed plasmonic modulator in a single metal layer, Science (2017). DOI: 10.1126/science.aan5953 
Journal reference: Science [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: ETH Zurich

Read more at:[url=]
Along the vines of the Vineyard.
With a forked tongue the snake singsss...
The path length of light in opaque media
November 10, 2017

[Image: thepathlengt.jpg]
Light on its way through a liquid: In case of a transparent liquid (left) light paths are straight lines. In case the liquid is made opaque through nanoparticles (right) light paths get more complicated through scattering. Some of the paths become longer, others shorter - on average though the length of light paths is the same as in the transparent case. Credit: Vienna University of Technology
A seemingly paradoxical prediction in physics has now been confirmed in an experiment: No matter whether an object is opaque or transparent, the average length of the light's paths through the object is always the same.

What happens when light passes through a glass of milk? It enters the liquid, is scattered unpredictably at countless tiny particles and exits the glass again. This effect makes milk appear white. The specific paths that the incident light beam takes depend, however, on the opacity of the liquid: A transparent substance will allow the light to travel through on a straight line, in a turbid substance the light will be scattered numerous times, travelling on more complicated zig-zag trajectories. But astonishingly, the average total distance covered by the light inside the substance is always the same.
Professor Stefan Rotter and his team (TU Wien, Austria) predicted this counter-intuitive result together with French colleagues three years ago. Now he and his collaborators from Paris verified this theory in an experiment. The results have now been published in the journal Science.
Particles and Waves
"We can get a simplified idea of this phenomenon when we imagine light as a stream of tiny particles," says Stefan Rotter. "The trajectories of the photons in the liquid depend on the number of obstacles they encounter."
In a clear, completely transparent liquid, the particles travel along straight lines, until they leave the liquid on the opposite side. In an opaque liquid, however, the trajectories are more complicated. The beam of light is scattered frequently along its way, it changes its direction many times, and it can only reach the opposite side after covering a long distance inside the opaque substance.
[Image: 1-thepathlengt.jpg]
Simulation results for light paths in circular areas with different degrees of opacity. Light comes in from the left with many different injection angles. Credit: Romain Pierret & Romolo Savo
But in a turbid liquid, there are also many photons, which will never reach the opposite side. They do not completely traverse the liquid, but just penetrate a little below the surface and after a few scattering events they exit the liquid again, so their trajectories are rather short. "It can be shown mathematically that, rather surprisingly, these two effects exactly balance," says Stefan Rotter. "The average path length inside the liquid is thus always the same—independent of whether the liquid is transparent or opaque."
At second glance, the situation is a bit more complicated: "We have to take into account that light travels through the liquid as a wave rather than as a particle along a specific trajectory," says Rotter. "This makes it more challenging to come up with a mathematical description, but as it turns out, this does not change the main result. Also if we consider the wave properties of light the mean length associated with light penetrating the liquid always stays the same, irrespective of how strongly the wave is scattered inside the medium."

Read more at:[/url][url=]
Along the vines of the Vineyard.
With a forked tongue the snake singsss...
A broadband achromatic metalens for focusing and imaging in the visible
  • Nature Nanotechnology (2018)
  • doi:10.1038/s41565-017-0034-6
[Image: 41565_2017_34_Fig1_HTML.jpg]

[Image: 41565_2017_34_Fig2_HTML.jpg]

[Image: 41565_2017_34_Fig3_HTML.jpg]

[Image: 41565_2017_34_Fig4_HTML.jpg]


A key goal of metalens research is to achieve wavefront shaping of light using optical elements with thicknesses on the order of the wavelength. Such miniaturization is expected to lead to compact, nanoscale optical devices with applications in cameras, lighting, displays and wearable optics. However, retaining functionality while reducing device size has proven particularly challenging. For example, so far there has been no demonstration of broadband achromatic metalenses covering the entire visible spectrum. Here, we show that by judicious design of nanofins on a surface, it is possible to simultaneously control the phase, group delay and group delay dispersion of light, thereby achieving a transmissive achromatic metalens with large bandwidth. We demonstrate diffraction-limited achromatic focusing and achromatic imaging from 470 to 670 nm. Our metalens comprises only a single layer of nanostructures whose thickness is on the order of the wavelength, and does not involve spatial multiplexing or cascading. While this initial design (numerical aperture of 0.2) has an efficiency of about 20% at 500 nm, we discuss ways in which our approach may be further optimized to meet the demand of future applications.

Single metalens focuses all colors of the rainbow in one point; opens new possibilities in virtual, augmented reality
January 1, 2018, Harvard John A. Paulson School of Engineering and Applied Sciences

[Image: singlemetale.jpg]
This flat metalens is the first single lens that can focus the entire visible spectrum of light -- including white light -- in the same spot and in high resolution. It uses arrays of titanium dioxide nanofins to equally focus wavelengths of light and eliminate chromatic aberration. Credit: Jared Sisler/Harvard SEAS
Metalenses—flat surfaces that use nanostructures to focus light—promise to revolutionize optics by replacing the bulky, curved lenses currently used in optical devices with a simple, flat surface. But, these metalenses have remained limited in the spectrum of light they can focus well. Now a team of researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) has developed the first single lens that can focus the entire visible spectrum of light—including white light—in the same spot and in high resolution. This has only ever been achieved in conventional lenses by stacking multiple lenses.

The research is published in Nature Nanotechnology.

Focusing the entire visible spectrum and white light - combination of all the colors of the spectrum—is so challenging because each wavelength moves through materials at different speeds. Red wavelengths, for example, will move through glass faster than the blue, so the two colors will reach the same location at different times resulting in different foci. This creates image distortions known as chromatic aberrations.

Cameras and optical instruments use multiple curved lenses of different thicknesses and materials to correct these aberrations, which, of course, adds to the bulk of the device.

"Metalenses have advantages over traditional lenses," says Federico Capasso, the Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS and senior author of the research. "Metalenses are thin, easy to fabricate and cost effective. This breakthrough extends those advantages across the whole visible range of light. This is the next big step."

The Harvard Office of Technology Development (OTD) has protected the intellectual property relating to this project and is exploring commercialization opportunities.

The metalenses developed by Capasso and his team use arrays of titanium dioxide nanofins to equally focus wavelengths of light and eliminate chromatic aberration. Previous research demonstrated that different wavelengths of light could be focused but at different distances by optimizing the shape, width, distance, and height of the nanofins. In this latest design, the researchers created units of paired nanofins that control the speed of different wavelengths of light simultaneously. The paired nanofins control the refractive index on the metasurface and are tuned to result in different time delays for the light passing through different fins, ensuring that all wavelengths reach the focal spot at the same time.

"One of the biggest challenges in designing an achromatic broadband lens is making sure that the outgoing wavelengths from all the different points of the metalens arrive at the focal point at the same time," said Wei Ting Chen, a postdoctoral fellow at SEAS and first author of the paper. "By combining two nanofins into one element, we can tune the speed of light in the nanostructured material, to ensure that all wavelengths in the visible are focused in the same spot, using a single metalens. This dramatically reduces thickness and design complexity compared to composite standard achromatic lenses."

"Using our achromatic lens, we are able to perform high quality, white light imaging. This brings us one step closer to the goal of incorporating them into common optical devices such as cameras," said Alexander Zhu, co-author of the study.

Next, the researchers aim to scale up the lens, to about 1 cm in diameter. This would open a whole host of new possibilities, such as applications in virtual and augmented reality.

[Image: 1x1.gif] Explore further: Flat lens to work across a continuous bandwidth allows new control of light

More information: A broadband achromatic metalens for focusing and imaging in the visible, Nature Nanotechnology (2018).

Journal reference: Nature Nanotechnology [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: Harvard John A. Paulson School of Engineering and Applied Sciences

Read more at:
Along the vines of the Vineyard.
With a forked tongue the snake singsss...

Quote:The metalenses developed by Capasso and his team 
use arrays of titanium dioxide nanofins 
to equally focus wavelengths of light and eliminate chromatic aberration. 

In this latest design, the researchers created units of paired nanofins 
that control the speed of different wavelengths of light simultaneously. 
The paired nanofins control the refractive index on the metasurface 
and are tuned to result in different time delays for the light passing through different fins, 
ensuring that all wavelengths reach the focal spot at the same time.

I wonder if there is a breakdown factor for TiO2 -- nanofins -- over time?
How stable is the metasurface in securing the nanofins?
If they are meant to be lenses,
I assume in a camera,
you had better not drop your camera. 
But then they would be cheap and easily interchangeble with replacements, 
if the camera design allows it.
Fascinating and superb innovation regardless.
Hope this BIG innovation to 3D camera to take images and DIRECTLY view them in 3D helmet glasses !!!

Bob... Ninja Assimilated
"The Morning Light, No sensation to compare to this, suspended animation, state of bliss, I keep my eyes on the circling sky, tongue tied and twisted just and Earth Bound Martian I" Learning to Fly Pink Floyd [Video:]
Kalter Rauch

Lately I've had recurring thoughts
about how the difference between
the speed of light in a vacuum
and the speed of light in a practical length* of fiber optics
can be measured.

* a classroom AFAIK

KR those are  'exceptional points' you make... >>>

Speed of light drops to zero at 'exceptional points'
January 31, 2018 by Lisa Zyga, 

[Image: stoppedlight.jpg]
Artistic image. Credit: pixabay
Light, which travels at a speed of 300,000 km/sec in a vacuum, can be slowed down and even stopped completely by methods that involve trapping the light inside crystals or ultracold clouds of atoms. Now in a new study, researchers have theoretically demonstrated a new way to bring light to a standstill: they show that light stops at "exceptional points," which are points at which two light modes come together and coalesce, in waveguides that have a certain kind of symmetry.

Unlike most other methods that are used to stop light, the new method can be tuned to work with a wide range of frequencies and bandwidths, which may offer an important advantage for future slow-light applications.

The researchers, Tamar Goldzak and Nimrod Moiseyev at the Technion – Israel Institute of Technology, along with Alexei A. Mailybaev at the Instituto de Matemática Pura e Aplicada (IMPA) in Rio de Janeiro, have published a paper on stopping light at exceptional points in a recent issue of Physical Review Letters.

As the researchers explain, exceptional points can be created in waveguides in a straightforward way, by varying the gain/loss parameters so that two light modes coalesce (combine into one mode). Although light stops at these exceptional points, in most systems much of the light is lost at these points. The researchers showed that this problem can be fixed by using waveguides with parity-time (PT) symmetry, since this symmetry ensures that the gain and loss are always balanced. As a result, the light intensity remains constant when the light approaches the exceptional point, eliminating losses.

To release the stopped light and accelerate it back up to normal speed, the scientists showed that the gain/loss parameters can simply be reversed. The most important feature of the new method, however, is that the exceptional points can be adjusted to work with any frequency of light, again simply by tuning the gain/loss parameters. The researchers also expect that this method can be used for other types of waves besides light, such as acoustic waves. They plan to further investigate these possibilities in the future.

[Image: 1x1.gif] Explore further: 'Exceptional points' give rise to counterintuitive physical effects

More information: Tamar Goldzak et al. "Light stops at exceptional points." Physical Review Letters. DOI: 10.1103/PhysRevLett.120.013901, Also at arXiv:1709.10172 [physics.optics]

Journal reference: Physical Review Letter

Read more at:

Now what's going on with the phenoms phonons ??? 

Scientists discover chiral phonons in a 2-D semiconductor crystal
February 2, 2018 by Glenn Roberts Jr., Lawrence Berkeley National Laboratory

[Image: 1-scientistsdi.gif]
The atomic motion in a 2-D material, tungsten disulfide, is shown in this animation. In this phonon mode (known as longitudinal optical mode or LO), the selenium atoms (yellow) rotate clockwise while the tungsten atoms (blue) are still. Credit: Hanyu Zhu, et al
A research team from the Department of Energy's Lawrence Berkeley National Laboratory (Berkeley Lab) has found the first evidence that a shaking motion in the structure of an atomically thin (2-D) material possesses a naturally occurring circular rotation.

This rotation could become the building block for a new form of information technology, and for the design of molecular-scale rotors to drive microscopic motors and machines.

The monolayer material, tungsten diselenide (WSe2), is already well-known for its unusual ability to sustain special electronic properties that are far more fleeting in other materials.

It is considered a promising candidate for a sought-after form of data storage known as valleytronics, for example, in which the momentum and wavelike motion of electrons in a material can be sorted into opposite "valleys" in a material's electronic structure, with each of these valleys representing the ones and zeroes in conventional binary data.

Modern electronics typically rely on manipulations of the charge of electrons to carry and store information, though as electronics are increasingly miniaturized they are more subject to problems associated with heat buildup and electric leaks.

The latest study, published online this week in the journal Science, provides a possible path to overcome these issues. It reports that some of the material's phonons, a term describing collective vibrations in atomic crystals, are naturally rotating in a certain direction.

This property is known as chirality – similar to a person's handedness where the left and right hand are a mirror image of each other but not identical. Controlling the direction of this rotation would provide a stable mechanism to carry and store information.

"Phonons in solids are usually regarded as the collective linear motion of atoms," said Xiang Zhang, the corresponding author of the study and senior scientist of the Materials Science Division at Lawrence Berkeley National Laboratory and professor at UC Berkeley. "Our experiment discovered a new type of so-called chiral phonons where atoms move in circles in an atomic monolayer crystal of tungsten diselenide."

[Image: 6-scientistsdi.jpg]
This diagram maps out atomic motion in separate phonon modes. At left (“LO” represents a longitudinal optical mode), selenium atoms exhibit a clockwise rotation while tungsten atoms stand still. At right (“LA” represents a longitudinal acoustic mode), tungsten atoms exhibit a clockwise rotation while selenium atoms rotate in a counterclockwise direction. Credit: Hanyu Zhu, et al
Hanyu Zhu, the lead author of the study and a postdoctoral researcher at Zhang's group, said, "One of the biggest advantage of chiral phonon is that the rotation is locked with the particle's momentum and not easily disturbed."

In the phonon mode studied, the selenium atoms appear to collectively rotate in a clockwise direction, while the tungsten atoms showed no motion. Researchers prepared a "sandwich" with four sheets of centimeter-sized monolayer WSe2 samples placed between thin sapphire crystals. They synced ultrafast lasers to record the time-dependent motions.
The two laser sources converged on a spot on the samples measuring just 70 millionths of a meter in diameter. One of the lasers was precisely switched between two different tuning modes to sense the difference of left and right chiral phonon activity.
A so-called pump laser produced visible, red-light pulses that excited the samples, and a probe laser produced mid-infrared pulses that followed the first pump pulse within one trillionth of a second. About one mid-infrared photon in every 100 million is absorbed by WSe2 and converted to a chiral phonon.
The researchers then captured the high-energy luminescence from the sample, a signature of this rare absorption event. Through this technique, known as transient infrared spectroscopy, researchers not only confirmed the existence of a chiral phonon but also accurately obtained its rotational frequency.
So far, the process only produces a small number of chiral phonons. A next step in the research will be to generate larger numbers of rotating phonons, and to learn whether vigorous agitations in the crystal can be used to flip the spin of electrons or to significantly alter the valley properties of the material. Spin is an inherent property of an electron that can be thought of as its compass needle – if it could be flipped to point either north or south it could be used to convey information in a new form of electronics called spintronics.
"The potential phonon-based control of electrons and spins for device applications is very exciting and within reach," Zhu said. "We already proved that phonons are capable of switching the electronic valley. In addition, this work allows the possibility of using the rotating atoms as little magnets to guide the spin orientation."
The chiral properties found in the study likely exist across a wide range of 2-D materials based on a similar patterning in their atomic structure, Zhu also noted, adding that the study could guide theoretical investigations of electron-phonon interactions and the design of materials to enhance phonon-based effects.
"The same principle works in all 2-D periodic structures with three-fold symmetry and inversion asymmetry" Zhu said. "The same principle covers a huge family of natural materials, and there are almost infinite possibilities for creating rotors at the molecular scale."
[Image: 1x1.gif] Explore further: Research team determines how electron spins interact with crystal lattice in nickel oxide
More information: Hanyu Zhu et al. Observation of chiral phonons, Science (2018). DOI: 10.1126/science.aar2711

Journal reference: Science [Image: img-dot.gif] [Image: img-dot.gif]

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Quote:"We were thinking about this regime based on the standard design guidelines, but the behavior we would see in the lab was different," said Marc Jankowski, lead author of the paper and a graduate student in the Ginzton Lab.
"We were seeing an improvement in performance, and we couldn't explain it."

Read more at:

New source found for ultra-short bursts of light

February 2, 2018 by Taylor Kubota, Stanford University

[Image: newsourcefou.jpg]
Alireza Marandi, left, and Marc Jankowski prepare to carry out experiments at the optical bench. Credit: L.A. Cicero
Although critical for varied applications, such as cutting and welding, surgery and transmitting bits through optical fiber, lasers have some limitations – namely, they only produce light in limited wavelength ranges. Now, researchers from the Ginzton Lab at Stanford University have modified similar light sources, called optical parametric oscillators, to overcome this obstacle.

Until now, these lesser-known light sources have been mostly confined to the lab because their setup leaves little room for error – even a minor jostle could knock one out of alignment. However, following a counterintuitive decision, the researchers may have found a solution to this weakness that could lead to smaller, lower-cost and more efficient sources of light pulses.
Their work, published Feb. 1 in Physical Review Letters, demonstrates a new way to produce femtosecond pulses – pulses measured by quadrillionths of a second – in desirable wavelength ranges using this light source. The technology could potentially lead to better detection of pollutants and diseases by merely scanning the air or someone's breath.
A counterintuitive innovation  Hi  Wave Guide @ Exceptional Points  (A.K.A Improvised ANU)
The light source these researchers study consists of an initial step where pulses of light from a traditional laser are passed through a special crystal and converted into a wavelength range that's difficult to access with conventional lasers. Then, a series of mirrors bounce the light pulses around in a feedback loop. When this feedback loop is synchronized to the incoming laser pulses, the newly converted pulses combine to form an increasingly strong output.
Traditionally, people could not convert much of the initial light pulses into the desired output with such a contraption. But to be effective in real-world applications, the group had to bump up that percentage.
"We needed higher conversion efficiency to prove it was a source worth studying," said Alireza Marandi, a staff member in the Ginzton Lab. "So we just said, 'OK, what are the knobs we have in the lab?' We turned one that made the mirrors reflect less light, which was against the standard guidelines, and the conversion efficiency doubled." The researchers published their initial experimental results two years ago in Optica.
Cranking up the power in a conventional design usually results in two undesirable outcomes: The pulses lengthen and the conversion efficiency drops. But in the new design, where the researchers significantly decreased the reflectivity of their mirrors, the opposite occurred.

"We were thinking about this regime based on the standard design guidelines, but the behavior we would see in the lab was different," said Marc Jankowski, lead author of the paper and a graduate student in the Ginzton Lab. "We were seeing an improvement in performance, and we couldn't explain it."
After more simulations and lab experiments, the group found that the key was not just making the mirrors less reflective but also lengthening the feedback loop. This lengthened the time it took for the light pulses to complete their loop and should have slowed them too much. But the lower reflectivity, combined with the time delay, caused the pulses to interact in unexpected ways, which pulled them back into synchronization with their incoming partners.
This unanticipated synchronization more than doubled the bandwidth of the output, which means it can emit a broader span of wavelengths within the range that is difficult to access with conventional lasers. For applications like detecting molecules in the air or in a person's breath, light sources with greater bandwidth can resolve more distinct molecules. In principle, the pulses this system produces could be compressed to as short as 18 femtoseconds, which can be used to study the behavior of molecules.
The decision to reduce the mirror reflectivity had the surprising consequence of making a formerly persnickety device more robust, more efficient and better at producing ultra-short light pulses in wavelength ranges that are difficult to access with traditional lasers.
Getting out of the lab
The next challenge is designing the device to fit in the palm of a hand.
"You talk with people who have worked with this technology for the past 50 years and they are very skeptical about its real-life applications because they think of these resonators as a very high-finesse arrangement that is hard to align and requires a lot of upkeep," said Marandi, who is also co-author of the paper. "But in this regime of operation these requirements are super-relaxed, and the source is super-reliable and doesn't need the extensive care required by standard systems."
This newfound design flexibility makes it easier to miniaturize such systems onto a chip, which could lead to many new applications for detecting molecules and remote sensing.
"Sometimes you completely reshape your understanding of systems you think you know," Jankowski said. "That changes how you interact with them, how you build them, how you design them and how useful they are. We've worked on these sources for years and now we've gotten some clues that will really help bring them out of the lab and into the world."

[Image: 1x1.gif] Explore further: Highly efficient, high-power short-pulse lasers based on Tm3+ doped materials
More information: Marc Jankowski et al. Temporal Simultons in Optical Parametric Oscillators, Physical Review Letters (2018). DOI: 10.1103/PhysRevLett.120.053904

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With a forked tongue the snake singsss...
the last article is fascinating


Quote:Cranking up the power in a conventional design usually results in two undesirable outcomes: 
The pulses lengthen 
and the conversion efficiency drops. 

But in the new design, 
where the researchers significantly decreased the reflectivity of their mirrors, 
the opposite occurred.

improv momentum

Quote:After more simulations and lab experiments, 
the group found that the key was not just making the mirrors less reflective Whip
but also lengthening the feedback loop. Jawdrop

improv on a roll of reliability and low maintenance 

Quote:... people very skeptical about its real-life applications,
because they think of these resonators as a very high-finesse arrangement,
that is hard to align and requires a lot of upkeep,"

"But in this regime of operation these requirements are super Smoke relaxed
and the source is super-reliable  Applause
and doesn't need the extensive care required by standard systems.  Nonono

Improv manufacturing real science into rapidly advancing technologies,
that the Chinese will steal and mass produce in low quality cheapo chips. 

Quote:This newfound design flexibility makes it easier to miniaturize such systems onto a chip, 
which could lead to many new applications for detecting molecules and remote sensing.

Intense laser experiments provide first evidence that light can stop electrons
February 7, 2018 by Hayley Dunning, Imperial College London

[Image: intenselaser.jpg]
Illustration of the effect. Credit: Imperial College London/Stuart Mangles
By hitting electrons with an ultra-intense laser, researchers have revealed dynamics that go beyond 'classical' physics and hint at quantum effects.

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Light controls two-atom quantum computation
February 7, 2018 by Olivia Meyer-Streng, Max Planck Institute of Quantum Optics

[Image: lightcontrol.jpg]
Fig. 1: Illustration of the experimental setup: From the right, single photons (bright red) impinge on an optical cavity in which two atoms (red bullets) are trapped. Because of the strong atom-light field coupling a long-range interaction is mediated between the atoms that can be used to realize gate operations. Following each gate operation, the resulting two-atom state is read out by resonantly probing the cavity transmission and the atomic fluorescence. Credit: MPQ, Quantum Dynamics Division
Some powerful rulers of the world may dream of the possibility to get in touch with their colleagues on different continents unnoticed by friends or foes. Someday, new quantum technologies could allow for making these wishes come true. Physicists around the world are working on the realization of large scale quantum networks in which single light quanta transfer (secret) quantum information to stationary nodes at large distances. Such quantum networks' fundamental building blocks are, for example, quantum repeaters that counteract the loss of quantum information over large distances, or quantum logic gates that are necessary for processing quantum information.

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Quote:In a paper published today in the journal Science, the team, led by Vladan Vuletic, the Lester Wolfe Professor of Physics at MIT, and Professor Mikhail Lukin from Harvard University, reports that it has observed groups of three photons interacting and, in effect, sticking together to form a completely new kind of photonic matter.

New form of light: Newly observed optical state could enable quantum computing with photons
February 15, 2018, Massachusetts Institute of Technology

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The setup. Credit: Science (2018). 10.1126/science.aao7293
Try a quick experiment: Take two flashlights into a dark room and shine them so that their light beams cross. Notice anything peculiar? The rather anticlimactic answer is, probably not. That's because the individual photons that make up light do not interact. Instead, they simply pass each other by, like indifferent spirits in the night.

But what if light particles could be made to interact, attracting and repelling each other like atoms in ordinary matter? One tantalizing, albeit sci-fi possibility:

Duel light sabers - beams of light that can pull and push on each other, making for dazzling, epic confrontations. Or, in a more likely scenario, two beams of light could meet and merge into one single, luminous stream.

It may seem like such optical behavior would require bending the rules of physics, but in fact, scientists at MIT, Harvard University, and elsewhere have now demonstrated that photons can indeed be made to interact - an accomplishment that could open a path toward using photons in quantum computing, if not in light sabers. Alium

In a paper published today in the journal Science, the team, led by Vladan Vuletic, the Lester Wolfe Professor of Physics at MIT, and Professor Mikhail Lukin from Harvard University, reports that it has observed groups of three photons interacting and, in effect, sticking together to form a completely new kind of photonic matter.
In controlled experiments, the researchers found that when they shone a very weak laser beam through a dense cloud of ultracold rubidium atoms, rather than exiting the cloud as single, randomly spaced photons, the photons bound together in pairs or triplets, suggesting some kind of interaction - in this case, attraction - taking place among them.
While photons normally have no mass and travel at 300,000 kilometers per second (the speed of light), the researchers found that the bound photons actually acquired a fraction of an electron's mass. These newly weighed-down light particles were also relatively sluggish, traveling about 100,000 times slower than normal noninteracting photons.
Vuletic says the results demonstrate that photons can indeed attract, or entangle each other. If they can be made to interact in other ways, photons may be harnessed to perform extremely fast, incredibly complex quantum computations.

"The interaction of individual photons has been a very long dream for decades," Vuletic says.
Vuletic's co-authors include Qi-Yung Liang, Sergio Cantu, and Travis Nicholson from MIT, Lukin and Aditya Venkatramani of Harvard, Michael Gullans and Alexey Gorshkov of the University of Maryland, Jeff Thompson from Princeton University, and Cheng Ching of the University of Chicago.
Biggering and biggering
Vuletic and Lukin lead the MIT-Harvard Center for Ultracold Atoms, and together they have been looking for ways, both theoretical and experimental, to encourage interactions between photons. In 2013, the effort paid off, as the team observed pairs of photons interacting and binding together for the first time, creating an entirely new state of matter.
In their new work, the researchers wondered whether interactions could take place between not only two photons, but more.
"For example, you can combine oxygen molecules to form O2 and O3 (ozone), but not O4, and for some molecules you can't form even a three-particle molecule," Vuletic says. "So it was an open question: Can you add more photons to a molecule to make bigger and bigger things?"
To find out, the team used the same experimental approach they used to observe two-photon interactions. The process begins with cooling a cloud of rubidium atoms to ultracold temperatures, just a millionth of a degree above absolute zero. Cooling the atoms slows them to a near standstill. Through this cloud of immobilized atoms, the researchers then shine a very weak laser beam - so weak, in fact, that only a handful of photons travel through the cloud at any one time.
The researchers then measure the photons as they come out the other side of the atom cloud. In the new experiment, they found that the photons streamed out as pairs and triplets, rather than exiting the cloud at random intervals, as single photons having nothing to do with each other.
In addition to tracking the number and rate of photons, the team measured the phase of photons, before and after traveling through the atom cloud. A photon's phase indicates its frequency of oscillation.
"The phase tells you how strongly they're interacting, and the larger the phase, the stronger they are bound together," Venkatramani explains. The team observed that as three-photon particles exited the atom cloud simultaneously, their phase was shifted compared to what it was when the photons didn't interact at all, and was three times larger than the phase shift of two-photon molecules. "This means these photons are not just each of them independently interacting, but they're all together interacting strongly."
Memorable encounters
The researchers then developed a hypothesis to explain what might have caused the photons to interact in the first place. Their model, based on physical principles, puts forth the following scenario: As a single photon moves through the cloud of rubidium atoms, it briefly lands on a nearby atom before skipping to another atom, like a bee flitting between flowers, until it reaches the other end.
If another photon is simultaneously traveling through the cloud, it can also spend some time on a rubidium atom, forming a polariton - a hybrid that is part photon, part atom. Then two polaritons can interact with each other via their atomic component. At the edge of the cloud, the atoms remain where they are, while the photons exit, still bound together. The researchers found that this same phenomenon can occur with three photons, forming an even stronger bond than the interactions between two photons.
"What was interesting was that these triplets formed at all," Vuletic says. "It was also not known whether they would be equally, less, or more strongly bound compared with photon pairs."
The entire interaction within the atom cloud occurs over a millionth of a second. And it is this interaction that triggers photons to remain bound together, even after they've left the cloud.
"What's neat about this is, when photons go through the medium, anything that happens in the medium, they 'remember' when they get out," Cantu says.
This means that photons that have interacted with each other, in this case through an attraction between them, can be thought of as strongly correlated, or entangled - a key property for any quantum computing bit.
"Photons can travel very fast over long distances, and people have been using light to transmit information, such as in optical fibers," Vuletic says. "If photons can influence one another, then if you can entangle these photons, and we've done that, you can use them to distribute quantum information in an interesting and useful way."
Going forward, the team will look for ways to coerce other interactions such as repulsion, where photons may scatter off each other like billiard balls.
"It's completely novel in the sense that we don't even know sometimes qualitatively what to expect," Vuletic says. "With repulsion of photons, can they be such that they form a regular pattern, like a crystal of light? Or will something else happen? It's very uncharted territory."
[Image: 1x1.gif] Explore further: Lens trick doubles odds for quantum interaction
More information: "Observation of three-photon bound states in a quantum nonlinear medium" Science (2018). … 1126/science.aao7293

Journal reference: Science [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: Massachusetts Institute of Technology

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Light is almost as anomalous as water.
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Researchers turn light upside down
February 23, 2018, Elhuyar Fundazioa

[Image: basqueresear.jpg]
Illustration of waves propagating away from a point-like source. Left: Regular wave propagation. Right: Wave propagation on a hyperbolic metasurface. Credit: P. Li, CIC nanoGUNE

Researchers from CIC nanoGUNE (San Sebastian, Spain) and collaborators have reported in Science the development of a so-called hyperbolic metasurface on which light propagates with completely reshaped wafefronts. This scientific achievement toward more precise control and monitoring of light is highly interesting for miniaturizing optical devices for sensing and signal processing.

Optical waves propagating away from a point source typically exhibit circular (convex) wavefronts. "Like waves on a water surface when a stone is dropped," says Peining Li, EU Marie Sklodowska-Curie fellow at nanoGUNE and first author of the paper. The reason for this circular propagation is that the medium through which light travels is typically homogeneous and isotropic, i.e., uniform in all directions.
Scientists had theoretically predicted that specifically structured surfaces can turn the wavefronts of light upside-down when it propagates along them. "On such surfaces, called hyberbolic metasurfaces, the waves emitted from a point source propagate only in certain directions, and with open (concave) wavefronts," explains Javier Alfaro, Ph.D. student at nanoGUNE and co-author of the paper. These unusual waves are called hyperbolic surface polaritons. Because they propagate only in certain directions, and with wavelengths that are much smaller than that of light in free space or standard waveguides, they could help to miniaturize optical devices for sensing and signal processing.
Now, the researchers have developed such a metasurface for infrared light. It is based on boron nitride, a graphene-like 2-D material, which was selected because of its ability to manipulate infrared light on extremely small length scales. This has applications in miniaturized chemical sensors or for heat management in nanoscale optoelectronic devices. The researchers directly observed the concave wavefronts with a special optical microscope.
Hyperbolic metasurfaces are challenging to fabricate, because an extremely precise structuring on the nanometer scale is required. Irene Dolado, Ph.D. student at nanoGUNE, and Saül Vélez, former postdoctoral researcher at nanoGUNE (now at ETH Zürich) mastered this challenge using electron beam lithography and etching of thin flakes of high-quality boron nitride provided by Kansas State University. "After several optimization steps, we achieved the required precision and obtained grating structures with gap sizes as small as 25 nm," Dolado says. "The same fabrication methods can also be applied to other materials, which could pave the way to realize artificial metasurface structures with custom-made optical properties," adds Saül Vélez.
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To see how the waves propagate along the metasurface, the researchers used a state-of the-art infrared nanoimaging technique that was pioneered by the nanoptics group at nanoGUNE. They first placed an infrared gold nanorod onto the metasurface.
Light is almost as anomalous as water. -EA
 "It plays the role of a stone dropped into water," says Peining Li.
[Image: ele-kelvinwake-2.png]
The nanorod concentrates incident infrared light into a tiny spot, which launches waves that then propagate along the metasurface. With the help of a so-called scattering-type scanning near-field microscope (s-SNOM) the researchers imaged the waves. "It was amazing to see the images. They indeed showed the concave curvature of the wavefronts that were propagating away form the gold nanorod, exactly as predicted by theory," says Rainer Hillenbrand, Ikerbasque Professor at nanoGUNE, who led the work.
The results promise nanostructured 2-D materials to become a novel platform for hyberbolic metasurface devices and circuits, and further demonstrate how near-field microscopy can be applied to unveil exotic optical phenomena in anisotropic materials and for verifying new metasurface design principles.
[Image: 1x1.gif] Explore further: Integrated metasurface converts colors of light over broadband inside a waveguide
More information: Peining Li et al, Infrared hyperbolic metasurface based on nanostructured van der Waals materials, Science (2018). DOI: 10.1126/science.aaq1704

Journal reference: Science [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: Elhuyar Fundazioa

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(01-03-2018, 03:05 AM)Vianova Wrote: ...

Quote:The metalenses developed by Capasso and his team 
use arrays of titanium dioxide nanofins 
to equally focus wavelengths of light and eliminate chromatic aberration. 

In this latest design, the researchers created units of paired nanofins 
that control the speed of different wavelengths of light simultaneously. 
The paired nanofins control the refractive index on the metasurface 
and are tuned to result in different time delays for the light passing through different fins, 
ensuring that all wavelengths reach the focal spot at the same time.

I wonder if there is a breakdown factor for TiO2 -- nanofins -- over time?
How stable is the metasurface in securing the nanofins?

If they are meant to be lenses,
I assume in a camera,

you had better not drop your camera. 
But then they would be cheap and easily interchangeble with replacements, 
if the camera design allows it.
Fascinating and superb innovation regardless.


Artificial eye: Researchers combine metalens with an artificial muscle Ninja

February 23, 2018, [url=]Harvard John A. Paulson School of Engineering and Applied Sciences

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Photo of the metalens (made of silicon) mounted on a transparent, stretchy polymer film, without any electrodes. The colorful iridescence is produced by the large number of nanostructures within the metalens. Credit: Harvard SEAS
Inspired by the human eye, researchers at the Harvard John A. Paulson School of Engineering and Applied Sciences (SEAS) have developed an adaptive metalens, that is essentially a flat, electronically controlled artificial eye. The adaptive metalens simultaneously controls for three of the major contributors to blurry images: focus, astigmatism, and image shift.

The research is published in Science Advances.
"This research combines breakthroughs in artificial muscle technology with metalens technology to create a tunable metalens that can change its focus in real time, just like the human eye," said Alan She, a graduate student at SEAS and first author of the paper. "We go one step further to build the capability of dynamically correcting for aberrations such as astigmatism and image shift, which the human eye cannot naturally do."
"This demonstrates the feasibility of embedded optical zoom and autofocus for a wide range of applications including cell phone cameras, eyeglasses and virtual and augmented reality hardware," said Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS and senior author of the paper. "It also shows the possibility of future optical microscopes, which operate fully electronically and can correct many aberrations simultaneously."
The Harvard Office of Technology Development has protected the intellectual property relating to this project and is exploring commercialization opportunities.
To build the artificial eye, the researchers first needed to scale-up the metalens.
[Image: 17-researchersc.jpg]
The adaptive metalens focuses light rays onto an image sensor. An electrical signal controls the shape of the metalens to produce the desired optical wavefronts (shown in red), resulting in better images. In the future, adaptive …more
Prior metalenses were about the size of a single piece of glitter. They focus light and eliminate spherical aberrations through a dense pattern of nanostructures, each smaller than a wavelength of light.
"Because the nanostructures are so small, the density of information in each lens is incredibly high," said She. "If you go from a 100 micron-sized lens to a centimeter sized lens, you will have increased the information required to describe the lens by ten thousand. Whenever we tried to scale-up the lens, the file size of the design alone would balloon up to gigabytes or even terabytes."
To solve this problem, the researchers developed a new doink-headto shrink the file size to make the metalens compatible with the technology currently used to fabricate integrated circuits. In a paper recently published in Optics Express, the researchers demonstrated the design and fabrication of metalenses up to centimeters or more in diameter.

"This research provides the possibility of unifying two industries: semiconductor manufacturing and lens-making, whereby the same technology used to make computer chips will be used to make metasurface-based optical components, such as lenses," said Capasso.
Next, the researchers needed to adhere the large metalens to an artificial muscle without compromising its ability to focus light. In the human eye, the lens is surrounded by ciliary muscle, which stretches or compresses the lens, changing its shape to adjust its focal length. Capasso and his team collaborated with David Clarke, Extended Tarr Family Professor of Materials at SEAS and a pioneer in the field of engineering applications of dielectric elastomer actuators, also known as artificial muscles.
The researchers chose a thin, transparent dielectic elastomer with low loss - meaning light travels through the material with little scattering - to attach to the lens. To do so, they needed to developed a platform to transfer and adhere the lens to the soft surface.

Movie shows metalens in motion, expanding and contracting due to an oscillating applied voltage, which causes the focal length to lengthen and shorten as well. Credit: Alan She/Harvard John A. Paulson School of Engineering and Applied Sciences
"Elastomers are so different in almost every way from semiconductors that the challenge has been how to marry their attributes to create a novel multi-functional device and, especially how to devise a manufacturing route," said Clarke. "As someone who worked on one of the first scanning electron microscopes (SEMs) in the mid 1960's, it is exhilarating to be a part of creating an optical microscope with the capabilities of an SEM, such as real-time aberration control."
The elastomer is controlled by applying voltage. As it stretches, the position of nanopillars on the surface of the lens shift. The metalens can be tuned by controlling both the position of the pillars in relation to their neighbors and the total displacement of the structures. The researchers also demonstrated that the lens can simultaneously focus, control aberrations caused by astigmatisms, as well as perform image shift.
Together, the lens and muscle are only 30 microns thick.
"All optical systems with multiple components - from cameras to microscopes and telescopes - have slight misalignments or mechanical stresses on their components, depending on the way they were built and their current environment, that will always cause small amounts of astigmatism and other aberrations, which could be corrected by an adaptive optical element," said She. "Because the adaptive metalens is flat, you can correct those aberrations and integrate different optical capabilities onto a single plane of control."
Next, the researchers aim to further improve the functionality of the lens and decrease the voltage required to control it.
[Image: img-dot.gif] Explore further: Flat lens to work across a continuous bandwidth allows new control of light
More information: "Adaptive metalenses with simultaneous electrical control of focal length, astigmatism, and shift" Science Advances (2018).

Provided by Harvard John A. Paulson School of Engineering and Applied Sciences
Along the vines of the Vineyard.
With a forked tongue the snake singsss...
Interesting and amazing advances in technology with the artificial eye .
No genetics involved ... no human tissues ... yet.

One of my favorite 3 minutes of old movies.
Blade Runner : Stereotypical Asian Eye Manufacturer
"I just do eyes"

Scientists create diodes made of light
March 16, 2018, National Physical Laboratory

[Image: 10-scientistscr.jpg]
Credit: National Physical Laboratory
Photonics researchers at the National Physical Laboratory (NPL) have achieved the extra-ordinary by creating a diode consisting of light that can be used, for the first time, in miniaturised photonic circuits, as published in Optica.

Dr. Pascal Del'Haye and his team at NPL have created an optical version of a diode that transmits light in one direction only, and can be integrated in microphotonic circuits. This small-scale integration has been a major challenge in photonics because existing optical diodes require bulky magnets.

NPL's ground-breaking work has overcome the limitation of diodes based on bulky magnets, by using light stored in tiny chip-based glass rings to form a diode.

Diodes are well known in electronic circuits. They transmit electric current in one direction but block the current in the backward direction. Diodes are essential components of nearly every electronic circuit and are used, for example, in battery chargers.

The novel technique was created by sending lots of light into a microresonator – a glass ring on a silicon chip, about the width of a human hair – and harnessing the circulating optical power to generate the diode effect.

Dr. Jonathan Silver, Higher Research Scientist at NPL, explains: "To create the optical diodes we used microrings that can store extremely large amounts of light. This meant that, even though we were only sending small amounts of light into these glass rings, the circulating power was comparable to the light generated by the flood lights in a whole football stadium—but confined into a device smaller than a human hair. The light intensities enable the formation of a diode via a light-with-light interaction called the Kerr effect."

In their experiments, they have shown that the electromagnetic field of clockwise circulating light in these glass rings effectively blocks any counterclockwise circulating light.

Pascal Del'Haye, Principal Research Scientist of the project emphasises: "These diodes will, for the first time, open the door to cheap and efficient optical diodes on microphotonic chips, and will pave the way for novel types of integrated photonic circuits which could be used for optical computing.

"They could also have significant impact on future optical telecommunication systems, for more efficient use of telecom networks."

Leonardo Del Bino, Doctoral Student on the project, said: "A remarkable property of this novel diode is that the performance improves if the forward propagating light field is increased. This is very important, for example, when using the diode to protect chip-integrated laser diodes from back reflections."

Beyond the use for optical diodes, NPL's research on interaction of counterpropagating light can enable new types of optical rotation sensors and optical memories.

[Image: 1x1.gif] Explore further: Researchers use sound waves to advance optical communication

More information: Leonardo Del Bino et al. Microresonator isolators and circulators based on the intrinsic nonreciprocity of the Kerr effect, Optica (2018). DOI: 10.1364/OPTICA.5.000279

Journal reference: Optica [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: National Physical Laboratory

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Scientists find holes in light by tying it in knots
August 1, 2018, University of Bristol

[Image: 35-scientistsfi.jpg]
Experimentally measured polarisation singularity trefoil knot. Credit: University of Bristol
A research collaboration including theoretical physicists from the University of Bristol and Birmingham has found a new way of evaluating how light flows through space—by tying knots in it.

Laser light may appear to be a single, tightly focused beam. In fact, it's an electromagnetic field, vibrating in an ellipse shape at each point in space. This multidirectional light is said to be 'polarised'.

The effect can be seen with polarised sunglasses, which only allow one direction of light to penetrate. By holding them up to the sky and rotating them, viewers will see darker and brighter patches as light flowing in different directions appears and disappears.

Now, scientists have been able to use holographic technology to twist a polarised laser beam into knots.

Professor Mark Dennis, from the University of Bristol's School of Physics and University of Birmingham's School of Physics and Astronomy, led the theoretical part of the research.

He said: "We are all familiar with tying knots in tangible substances such as shoelaces or ribbon. A branch of mathematics called 'knot theory' can be used to analyse such knots by counting their loops and crossings.

"With light, however, things get a little more complex. It isn't just a single thread-like beam being knotted, but the whole of the space or 'field' in which it moves.

"From a maths point of view, it isn't the knot that's interesting, it's the space around it. The geometric and spatial properties of the field are known as its topology."

In order to analyse the topology of knotted light fields, researchers from universities in Bristol, Birmingham, Ottowa and Rochester used polarised light beams to create structures known as 'polarisation singularities'.

Discovered by Professor John Nye in Bristol over 35 years ago, polarisation singularities occur at points where the polarisation ellipse is circular, with other polarisations wrapping around them. In 3 dimensions, these singularities occur along lines, in this case creating knots.

The team were able to create knots of much greater complexity than previously possible in light and analysed them in fine detail.

Professor Dennis added: "One of the purposes of topology is to talk about showing data in terms of lines and surfaces. The real-world surfaces have a lot more holes than the maths predicted."

[Image: 1x1.gif] Explore further: Tying light in knots

More information: Hugo Larocque et al. Reconstructing the topology of optical polarization knots, Nature Physics (2018). DOI: 10.1038/s41567-018-0229-2

Journal reference: Nature Physics [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: University of Bristol

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'Optical rocket' created with intense laser light LilD

September 14, 2018, University of Nebraska-Lincoln

[Image: opticalrocke.jpg]
One of the lasers at the Extreme Light Laboratory at the University of Nebraska-Lincoln, where a recent experiment accelerated electrons to near the speed of light. Credit: University of Nebraska-Lincoln
In a recent experiment at the University of Nebraska–Lincoln, plasma electrons in the paths of intense laser light pulses were almost instantly accelerated close to the speed of light.

Physics professor Donald Umstadter, who led the research experiment that confirmed previous theory, said the new application might aptly be called an "optical rocket" because of the tremendous amount of force that light exerted in the experiment. The electrons were subjected to a force almost a trillion-trillion-times greater than that felt by an astronaut launched into space.

"This new and unique application of intense light can improve the performance of compact electron accelerators," he said. "But the novel and more general scientific aspect of our results is that the application of force of light resulted in the direct acceleration of matter."

The optical rocket is the latest example of how the forces exerted by light can be used as tools, Umstadter said.

Normal intensity light exerts a tiny force whenever it reflects, scatters or is absorbed. One proposed application of this force is a "light sail" that could be used to propel spacecraft. Yet because the light force is exceedingly small in this case, it would need to be exerted continuously for years for the spacecraft to reach high speed.

[Image: 1-opticalrocke.jpg]
Grigory Golovin. Credit: University of Nebraska-Lincoln
Another type of force arises when light has an intensity gradient. One application of this light force is an "optical tweezer" that Is used to manipulate microscopic objects. Here again, the force is exceedingly small.

In the Nebraska experiment, the laser pulses were focused in plasma. When electrons in the plasma were expelled from the paths of the light pulses by their gradient forces, plasma waves were driven in the wakes of the pulses, and electrons were allowed to catch the wakefield waves, which further accelerated the electrons to ultra-relativistic energy. The new application of intense light provides a means to control the initial phase of wakefield acceleration and improve the performance of a new generation of compact electron accelerators, which are expected to pave the way for a range of applications that were previously impractical because of the enormous size of conventional accelerators.

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New understanding of light allows researchers to see around corners
September 17, 2018, University of Central Florida

[Image: 6-newunderstan.jpg]
Aristide Dogariu, a University of Central Florida Pegasus Professor of Optics and Photonics, and his colleagues have found a way to passively sense an object even when direct vision is impeded -- around the corner. Credit: UCF, Karen Norum

Covert sensing of objects around a corner may soon become a reality.

Aristide Dogariu, a University of Central Florida Pegasus Professor of Optics and Photonics, and his colleagues published a paper in Nature Communications this month demonstrating how to passively sense an object even when direct vision is impeded.

It's a bit complicated, but the new sensing method the UCF team developed could lends itself to a number of practical applications, including use in defense, surveillance, search and rescue and medicine.

Imagine trying to see something around a corner. This is easily done with mirrors, but imagine that light from the object can only reach the detector after it bounces off a diffusing wall that acts like a shattered mirror. Even though light looks totally dispersed, some of its initial properties do not completely vanish. Dogariu and his colleagues were able to measure subtle similarities in the scattered light, undo the effects of this broken mirror, and get an idea of what lies around the corner.

"The fact that fundamental properties are not completely destroyed when light bounces off a diffuse medium like a wall can be used in so many different ways," says Dogariu. "The question is, how much information you can still recover through this broken mirror-like surface."

When a digital picture is taken, the spatial distribution of light across an object is mapped point by point, pixel by pixel, onto the plane of the camera. However, in its propagation from object to the camera, properties of light can be affected by what the light reflects off of. When it reflects off of a mirror, a clear image can be produced. But when it is reflected off of a shattered mirror, for example, the direction of light is altered and only a distorted version of the image can be seen.

Dogariu and his colleagues have found a way to describe how this measure of similarity between two points, called spatial coherence of light, transfers in a reflection from a diffuse wall. By learning how the light transforms, the researchers can determine where the light came from. Dogariu describes their findings as an aspect of light propagation that has simply been overlooked before. By undoing the effects of the diffusing wall, Dogariu and his colleagues have eliminated the need to control the light that illuminates the target object.

This is the first time that there has been a practical demonstration of passively detecting an object around a corner in this way.

The technique does not recover a complete image but collects more than enough information needed for task oriented surveillance.

"The potential of this technique goes beyond sensing," says George Atia, a professor in EECS and member of a larger UCF team funded under Defense Advanced Research Projects Agency's Revolutionary Enhancement of Visibility by Exploiting Active Light-fields project that initiated this research. "Based on results of our recent simulations, we envision that non-line-of-sight, passive imaging of complex scenes could be achieved by data fusing that combines spatial coherence with additional intensity information."

Until now, detection of objects around a corner has only been possible by emitting light toward the object and modifying some of its properties, say by sending a pulse of light, the light will bounce off the diffuse wall, onto the object, to the diffuse wall again, and back to the detector. The amount of time the light takes to return to the detector is then used to triangulate the position of the object. The problem with such methods is that the emission of light discloses the intent to see, which can be problematic in covert situations.

The new sensing method is not specific to light. It could be applied for example to infrared or microwaves radiation.

The other co-authors on the Nature Communications paper are Mahed Batarseh, Sergey Sukhov, Zhean Chen, Heath Gemar, Roxana Rezvani from UCF.

[Image: 1x1.gif] Explore further: By listening to optical 'noise,' researchers discover new way to track hidden objects

Journal reference: Nature Communications [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: University of Central Florida

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That is kinda KEWL.

One might not notice a waver/shiver in the light ahead of a person walking down the street, so if they have the physics of HOW the visible spectrum is 'disturbed' to be able to capture what is in one direction or the the other ( could be if tetrahedron you could do 3D acquisition ) then be able to capture an IMAGE of the 'scene' would certainly be KEWL.

The previous article was also AWESOME, we now KNOW light sails to the stars do NOT need a LASER on an asteroid behind the craft; it can be attached to the craft as it makes SURE the electrons exit the plasma out a ROCKET type exhaust pipe.

Great posts as always.   Worship Applause

Bob... Ninja Assimilated
"The Morning Light, No sensation to compare to this, suspended animation, state of bliss, I keep my eyes on the circling sky, tongue tied and twisted just and Earth Bound Martian I" Learning to Fly Pink Floyd [Video:]
Groundbreaking new technology could allow 100-times-faster internet by harnessing twisted light beams
October 24, 2018, RMIT University

[Image: 23-newtechnolog.jpg]
The miniature OAM nano-electronic detector decodes twisted light. Credit: RMIT Uinversity
Broadband fiber-optics carry information on pulses of light, at the speed of light, through optical fibers. But the way the light is encoded at one end and processed at the other affects data speeds.

This world-first nanophotonic device, just unveiled in Nature Communications, encodes more data and processes it much faster than conventional fiber optics by using a special form of 'twisted' light.

Dr. Haoran Ren from RMIT's School of Science, who was co-lead author of the paper, said the tiny nanophotonic device they have built for reading twisted light is the missing key required to unlock super-fast, ultra-broadband communications.

"Present-day optical communications are heading towards a 'capacity crunch' as they fail to keep up with the ever-increasing demands of Big Data," Ren said.

"What we've managed to do is accurately transmit data via light at its highest capacity in a way that will allow us to massively increase our bandwidth."

Current state-of-the-art fiber-optic communications, like those used in Australia's National Broadband Network (NBN), use only a fraction of light's actual capacity by carrying data on the colour spectrum.

New broadband technologies under development use the oscillation, or shape, of light waves to encode data, increasing bandwidth by also making use of the light we cannot see.

This latest technology, at the cutting edge of optical communications, carries data on light waves that have been twisted into a spiral to increase their capacity further still. This is known as light in a state of orbital angular momentum, or OAM.

In 2016 the same group from RMIT's Laboratory of Artificial-Intelligence Nanophotonics (LAIN) published a disruptive research paper in Science journal describing how they'd managed to decode a small range of this twisted light on a nanophotonic chip. But technology to detect a wide range of OAM light for optical communications was still not viable, until now.

"Our miniature OAM nano-electronic detector is designed to separate different OAM light states in a continuous order and to decode the information carried by twisted light," Ren said.

"To do this previously would require a machine the size of a table, which is completely impractical for telecommunications. By using ultrathin topological nanosheets measuring a fraction of a millimeter, our invention does this job better and fits on the end of an optical fiber."

LAIN Director and Associate Deputy Vice-Chancellor for Research Innovation and Entrepreneurship at RMIT, Professor Min Gu, said the materials used in the device were compatible with silicon-based materials use in most technology, making it easy to scale up for industry applications.

"Our OAM nano-electronic detector is like an 'eye' that can 'see' information carried by twisted light and decode it to be understood by electronics. This technology's high performance, low cost and tiny size makes it a viable application for the next generation of broadband optical communications," he said.

"It fits the scale of existing fiber technology and could be applied to increase the bandwidth, or potentially the processing speed, of that fiber by over 100 times within the next couple of years. This easy scalability and the massive impact it will have on telecommunications is what's so exciting."

Gu said the detector can also be used to receive quantum information sent via twisting light, meaning it could have applications in a whole range of cutting edge quantum communications and quantum computing research.

"Our nano-electronic device will unlock the full potential of twisted light for future optical and quantum communications," Gu said.

[Image: 1x1.gif] Explore further: Twisted light could dramatically boost internet speeds

More information: Zengji Yue et al, Angular-momentum nanometrology in an ultrathin plasmonic topological insulator film,Nature Communications (2018). DOI: 10.1038/s41467-018-06952-1 

Journal reference: Nature Communications [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: RMIT University

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Explore further: Twisted light could dramatically boost internet speeds

I followed that thread at physorg as it branched out through photonics, nanomaterials, etc.

Paul... on the road to Damascus.

KR by 2020 envision Humanity as Arrow  itza resolves to a ' Type 2 Civilization '.

Quote:"It fits the scale of existing fiber technology and could be applied to increase the bandwidth, or potentially the processing speed, of that fiber by over 100 times within the next couple of years. This easy scalability and the massive impact it will have on telecommunications is what's so exciting."

Gu said the detector can also be used to receive quantum information sent via twisting light, meaning it could have applications in a whole range of cutting edge quantum communications and quantum computing research.

"Our nano-electronic device will unlock the full potential of twisted light for future optical and quantum communications," Gu said.

Micro-nano Macro Meta Material Magic 

pulsed polarized photonic pinwheels palette 
Quote:[Image: spinningthel.jpg]
Spinning the light: The world's smallest optical gyroscope
Gyroscopes are devices that help vehicles, drones, and wearable and handheld electronic devices know their orientation in three-dimensional space. They are commonplace in just about every bit of technology we rely on every ...
[Image: 1x1.gif]5 hours ago in Optics & Photonics

quantum qubit quacky qutrit quickening

exponential expanding electro-magnetic envelope evolves

As our first interstellar probes leave our solar sytem as of this thread...
Quote:[Image: 5bd1cedf99762.jpg]
Tiny diamond invention could help launch rockets into space
Scientists at ANU have invented tiny diamond electronic parts that could outperform and be more durable than today's devices in high-radiation environments such as rocket engines, helping to reach the next frontier in space.
[Image: 1x1.gif]9 hours ago in Condensed Matter

phase 2 is by logic of moore's law... gonna be sudden in human historical terms.

Quote:I followed that thread at physorg as it branched out through photonics, nanomaterials, etc.

[Image: damned.gif]

Don't fret...  Guitar

Team study breaks Forster resonant energy transfer (FRET) distance limit
October 25, 2018, City College of New York

[Image: ccnystudybre.jpg]
Schematic of the long-range energy transfer between donor and acceptor molecules enhanced by the metamaterial. Credit: Visakh Menon
Using engineered nanocomposite structures called metamaterials, a City College of New York-led research team reports the ability to measure a significant increase in the energy transfer between molecules. Reported in the journal ACS Photonics, this breakthrough breaks the Förster resonance energy transfer (FRET) distance limit of ~10-20 nanometers, and leads to the possibility of measuring larger molecular assemblies.

And since FRET is a staple technique in many biological and biophysical fields, this new development could benefit pharmaceuticals, for instance.

"Energy transfer between molecules plays a central role in phenomena such as photosynthesis and is also used as a spectroscopic ruler for identifying structural changes of molecules," said Vinod Menon, professor of physics in City College's Division of Science. "However, the process of energy transfer is usually limited in the distance over which it occurs, typically reaching 10 to 20 nm."

But in the study reported by Menon's research group in ACS Photonics, the authors demonstrate significant increase in theenergy transfer distance (> 15x) - reaching ~ 160 nm. This is accomplished by using a metamaterial that undergoes a topological transition.

The present work sets the stage for the use of spectroscopic rulers for studying a wide array of larger molecular systems which has not been previously possible using standard FRET technique.

 Explore further: Scientists develop new hybrid energy transfer system

Journal reference: ACS Photonics [Image: img-dot.gif] [Image: img-dot.gif]
Provided by: City College of New York

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Researchers develop small device that bends light to generate new radiation
October 25, 2018 by Morgan Sherburne, University of Michigan

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A research team led by University of Michigan physicists have developed a way to generate synchrotron using a device the size of a match head. Typically, synchrotron radiation is generated at facilities the size of several football fields. Credit: Austin Thomason/Michigan Photography
University of Michigan physicists have led the development of a device the size of a match head that can bend light inside a crystal to generate synchrotron radiation in a lab.

When physicists bend very intense beams of charged particles in circular orbits near the speed of light, this bending throws off bits of light, or X-rays, called synchrotron radiation. The U-M-led researchers used their device to bend visible light to produce light with a wavelength in the terahertz range. This range of wavelength is considerably larger than that of visible light, but much smaller than the waves your microwave produces—and can penetrate clothing.

Synchrotron radiation is usually generated at large-scale facilities, which are typically the size of several football stadiums. Instead, U-M researchers Roberto Merlin and Meredith Henstridge's team developed a way to produce synchrotron radiation by printing a pattern of microscopic gold antennae on the polished face of a lithium tantalate crystal, called a metasurface. The U-M team, which also included researchers from Purdue University, used a laser to pulse light through the pattern of antennae, which bent the light and produced synchrotron radiation.

"Instead of using lenses and spatial light modulators to perform this kind of experiment, we figured out by simply patterning a surface with a metasurface, you can achieve a similar end," said Merlin, professor of physics and electrical engineering and computer science. "In order to get light to curve, you have to sculpt every piece of the light beam to a particular intensity and phase, and now we can do this in an extremely surgical way."

Anthony Grbic, U-M professor of electrical engineering and computer science, led the team that designed the metasurface with former doctoral student Carl Pfeiffer developing the metasurface.

The metasurface is composed of roughly 10 million tiny boomerang-shaped antennae. Each antenna is considerably smaller than the wavelength of the impinging light, said Henstridge, lead author of the study. The researchers use a laser that produces "ultrashort" bursts or pulses of light which last for one trillionth of a second. The array of antennae causes the light pulse to accelerate along a curved trajectory inside the crystal.

[Image: 183-researchersd.jpg]
Microscopic device that bends light. Credit: Austin Thomason/Michigan Photography
The light pulse creates a collection of electric dipoles—or, a group of positive and negative charge pairs. This dipole collection accelerates along the curved trajectory of the light pulse, resulting in the emission of synchrotron radiation, according to Henstridge, who earned her doctoral degree at U-M and is now a postdoctoral scientist at the Max Planck Institute for the Structure and Dynamics of Matter in Hamburg, Germany.

The researchers' device produces synchrotron radiation that contains many terahertz frequencies because the light pulses travel just a fraction of a circle. But they hope to refine their device so that the light pulse revolves continuously along a circular path, producing synchrotron radiation at a single terahertz frequency.

The scientific community uses single-frequency terahertz sources to study the behavior of atoms or molecules within a given solid, liquid or gas. Commercially, terahertz sources are used to scan items hidden in clothing and packaging crates. Drugs, explosive and toxic gases all have unique "fingerprints" in the terahertz range that could be identified using terahertz spectroscopy.

The device's uses aren't limited to the security industry.

"Terahertz radiation is useful for imaging in the biomedical sciences," Henstridge said. "For instance, it has been used to distinguish between cancerous and healthy tissue. An on-chip, single-frequency terahertz source, such as a tiny light-drivensynchrotron such as our device, can allow for new advancements in all of these applications."

[Image: 1x1.gif] Explore further: Scientists advance technique for developing novel light beams from synchrotron radiation

Provided by: University of Michigan

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Its a write Itself-torque
Its a right itself-torque
Itza rite Its self-torque  

Quote:This resulted in a beam that looked like a corkscrew with a gradually changing twist. 
More wine?
JUNE 28, 2019 REPORT
New property of light discovered
by Bob Yirka ,
[Image: lightbeam.jpg]Credit: CC0 Public Domain
A team of researchers affiliated with several institutions in Spain and the U.S. has announced that they have discovered a new property of light—self-torque. In their paper published in the journal Science, the group describes how they happened to spot the new property and possible uses for it.

Scientists have long known about such properties of light as wavelength. More recently, researchers have found that light can also be twisted, a property called angular momentum. Beams with highly structured angular momentum are said to have orbital angular momentum (OAM), and are called vortex beams. They appear as a helix surrounding a common center, and when they strike a flat surface, they appear as doughnut-shaped. In this new effort, the researchers were working with OAM beams when they found the light behaving in a way that had never been seen before.
The experiments involved firing two lasers at a cloud of argon gas—doing so forced the beams to overlap, and they joined and were emitted as a single beam from the other side of the argon cloud. The result was a type of vortex beam. The researchers then wondered what would happen if the lasers had different orbital angular momentum and if they were slightly out of sync. This resulted in a beam that looked like a corkscrew with a gradually changing twist. And when the beam struck a flat surface, it looked like a crescent moon. The researchers noted that looked at another way, a single photon at the front of the beam was orbiting around its center more slowly than a photon at the back of the beam. The researchers promptly dubbed the new property self-torque—and not only is it a newly discovered property of light, it is also one that has never even been predicted.
PIPEnter fullscreen


A new property of light beams, the self-torque of light, which is associated to a temporal variation of the orbital angular momentum. Extreme-ultraviolet ultrafast pulses with self-torque are generated through high harmonic generation. Credit: JILA (USA) Rebecca Jacobson, Servicio de Produccion e Innovacion Digital – Universidad de Salamanca (Spain)
The researchers suggest that it should be possible to use their technique to modulate the orbital angular momentum of light in ways very similar to modulating frequencies in communications equipment. This could lead to the development of novel devices that make use of manipulating extremely tiny materials.


Explore further
Multicolored light twists in new knotted ways[/size]

More information: Laura Rego et al. Generation of extreme-ultraviolet beams with time-varying orbital angular momentum, Science (2019). DOI: 10.1126/science.aaw9486
Journal information: Science

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AUGUST 5, 2019
Corkscrew photons may leave behind a spontaneous twist
by Chris Cesare, Joint Quantum Institute
[Image: corkscrewpho.jpg]A new prediction argues that some materials might experience a torque when they are hotter than their surroundings. Credit: E. Edwards/JQI
Everything radiates. Whether it's a car door, a pair of shoes or the cover of a book, anything hotter than absolute zero (i.e., pretty much everything) is constantly shedding radiation in the form of photons, the quantum particles of light.

A twin process—absorption—is usually also present. As photons carry away energy, passers-by from the environment can be absorbed to replenish it. When absorption and emission occur at the same rate, scientists say that an object is in equilibrium with its environment. This often means that object and environment share the same temperature.
Far away from equilibrium, new behaviors can emerge. In a paper published August 1, 2019 as an Editors' Suggestion in the journal Physical Review Letters, scientists at JQI and Michigan State University suggest that certain materials may experience a spontaneous twisting force if they are hotter than their surroundings.
"The fact that a material might feel a torque due to a temperature difference with the environment is very unusual," says lead author Mohammad Maghrebi, a former JQI postdoctoral researcher who is now an assistant professor at Michigan State University.
The effect, which hasn't yet been observed in an experiment, is predicted to arise in a thin ribbon of a material called a topological insulator (TI)—something that allows electrical current to flow on its surface but not through its innards.
In this case, the researchers made two additional assumptions about the TI. One is that it is hotter than its environment. And another is that the TI has some magnetic impurities that affect the behavior of electrons on its surface.
These magnetic impurities interact with a quantum property of the electrons called spin. Spin is part of the basic character of an electron, much like electric charge, and it describes the particle's intrinsic angular momentum—the tendency of an object to continue rotating. Photons, too, can carry angular momentum.
Although electrons don't physically rotate, they can still gain and lose angular momentum, albeit only in discrete chunks. Each electron has two spin values—up and down—and the magnetic impurities ensure that one value sits at a higher energy than the other. In the presence of these impurities, electrons can flip their spin from up to down and vice versa by emitting or absorbing a photon that carries the right amount of energy and angular momentum.

Maghrebi and two colleagues, JQI Fellows Jay Deep Sau and Alexey Gorshkov, showed that radiation emanating from this kind of TI carries angular momentum skewed in one rotational direction, like a corkscrew that twists clockwise. The material gets left with a deficit of angular momentum, causing it to feel a torque in the opposite direction (in this example, counterclockwise).
The authors say that TIs are ideal for spotting this effect because they play host to the right kind of interaction between electrons and light. TIs already link electron spin with the momentum of their motion, and it's through this motion that electrons in the material ordinarily absorb and emit light.
If an electron on the surface of this particular kind of TI starts with its spin pointing up, it can shed energy and angular momentum by changing its spin from up to down and emitting a photon. Since the TI is hotter than its environment, electrons will flip from up to down more often than the reverse. That's because the environment has a lower temperature and lacks the energy to replace the radiation coming from the TI. The result of this imbalance is a torque on the thin TI sample, driven by the random emission of radiation.
Future experiments might observe the effect in one of two ways, the authors say. The most likely method is indirect, requiring experimenters to heat up a TI by running a current through it and collecting the emitted light. By measuring the average angular momentum of the radiation, an experiment might detect the asymmetry and confirm one consequence of the new prediction.
A more direct—and likely more difficult—observation would involve actually measuring the torque on the thin film by looking for tiny rotations. Maghrebi says that he's brought up the idea to several experimentalists. "They were not horrified by having to measure something like a torque, but, at the same time, I think it really depends on the setup," he says. "It certainly didn't sound like it was impossible."


Explore further
Mechanical vibration generated by electron spins[/size]

More information: Fluctuation-Induced Torque on a Topological Insulator out of Thermal Equilibrium, Physical Review Letters (2019). … ysRevLett.123.055901
Journal information: Physical Review Letters [/url]

Provided by [url=]Joint Quantum Institute
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