Harvard researchers have succeeded in creating a new material that causes light to act in entirely new ways. This discovery can help researchers learn more about the properties of light, but also may have some practical applications.

Light is ubiquitous and vital, but also incredibly strange – and it’s possible we’ll never exhaust the opportunities to learn more about it.

Case in point: researchers at Harvard have developed a material that can generate and maintain completely new and more complex states of light.

The tool uses polarisation to generate structures such as swirling vortices, spirals, and corkscrews that not only help explore light’s properties, but also have potential practical applications, such as high-powered imaging.

Discoveries about light are still being made. It was only in 2015 that scientists took the first-ever photograph of light behaving as both a particle and a wave.

And it hasn’t even been that long – just 1992, 25 years ago – since light was discovered to have orbital angular momentum.

This is angular momentum based on the shape of its wavefront, rather than its orientation. The new tool – a type of metasurface – uses this along with second type of angular momentum called spin angular momentum (also known as circular polarisation).

“Think about orbital angular momentum and circular polarisation like the motion of a planet,” writes Harvard’s Leah Burrows in a statement.

“Circular polarisation is the direction in which a planet rotates on its axis while orbital momentum describes how the planet orbits the sun.”

It’s previously been established that a single beam of light can exhibit both types of angular momentum, and that connecting them and using polarisation to control the OAM can result in beams with new and complex shapes, such as the aforementioned corkscrew.

According to the researchers, until now there was a significant limit on this. Only certain polarisations could connect to certain OAMs.

This is where the new tool comes in – it allows any polarisation to be converted to any OAM, which means it can create spirals and corkscrews and vortices of any size.

“This is a completely new optical component,” said co-first researcher Antonio Ambrosio, Principal Scientist at Harvard Center for Nanoscale Systems.

“Some metasurfaces are iterations or more efficient, more compact versions of existing optical devices but, this arbitrary spin-to-orbital conversion cannot be done with any other optical device.

“There is nothing in nature as well that can do this and produce these states of light.”

(Capasso Lab/Harvard SEAS)

Orbital angular momentum already has several proposed uses, such as high-speed data transfer, and encoded communications. Researchers have even figured out how to transmit the OAM of individual photons using entanglement.

Other previously proposed applications include the manipulation of microscopic objects, and imaging systems.

This is where Harvard’s device could prove practical. The metasurface could be used to shape optical tweezers to manipulate objects as small as atoms and molecules. Changing the polarisation could change the direction of the applied force.

It could also be used for high-powered imaging, because the black hole down the centre of the vortex can be used to take images of features smaller than the diffraction limit, the researchers said.

“There is interest in these beams in quantum optics and quantum information,” explained co-first researcher Noah Rubin.

“On the more applied side, these beams could find application in free-space optical communication, especially in scattering environments where this is usually difficult.

“Moreover, it has been recently shown that similar elements can be incorporated into lasers, directly producing these novel states of light. This may lead to unforeseen applications.”

Harvard has legally protected all IP related to the project and is currently seeking commercialisation opportunities. The research itself has been published in the journal Science.

Via Futurism.

Typically, optical waves exhibit circular wavefronts when they propagate away from a source point. In general, they act in the same manner as when ripples are formed when you drop an object into water.

However, there are specific structures, referred to as metasurfaces, that could turn light upside down as it propagates along them.

Scientists call these unusual wavefronts hyperbolic surface polaritons.

In a studypublished in the journal Science, the CIC nanoGUNE researchers from Spain said that their scientific achievement could have practical application in studies aimed at controlling and monitoring lights.

“Metasurfaces with strongly anisotropic optical properties can support deep subwavelength-scale confined electromagnetic waves (polaritons), which promise opportunities for controlling light in photonic and optoelectronic applications,” the researchers wrote in their paper.

The metasurface created by the Spanish researchers is based on 2D boron nitride (BN). They firmly believe that this new type of surface could be used to develop miniature chemical sensors or may be applied in managing heat for nanoscale optoelectronic devices.

Illustration of waves propagating along a standard surface (Left) and a metasurface (Right) | CIC nanoGUNE via Phys.org | Phys.org

For years, scientists had theoretically predicted that a metasurface could turn light upside down when it propagates along it.

“On such surfaces, called hyperbolic metasurfaces, the waves emitted from a point source propagate only in certain directions, and with open (concave) wavefronts,” Javier Alfaro, a Ph.D. student at nanoGune and co-author of the paper, was quoted as saying.

According to Alfaro, the hyperbolic surface polaritons have wavelengths that are much “smaller than that of light in free space or standard waveguides,” and they only propagate in specific directions.

However, creating a metasurface where the surface polaritons could propagate is no easy feat as it requires extremely precise structuring on the nanometer scale.

To accomplish this, Alfaro and his colleagues used a graphene-like 2D material called boron nitride. Apparently, boron nitride can manipulate infrared light on a microscopic scale.

“We developed a mid-infrared hyperbolic metasurface by nanostructuring a thin layer of hexagonal boron nitride that supports deep subwavelength-scale phonon polaritons that propagate with in-plane hyperbolic dispersion,” Alfaro explained in their study.

The researchers also reportedly used electron beam lithography and etching of thin flakes of high-quality boron nitride from Kansas State University to create the metasurface.

“After several optimization steps, we achieved the required precision and obtained grating structures with gap sizes as small as 25 nm,” Irene Dolado, another Ph.D. student at nanoGUNE, explained.

“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,” Saül Vélez, a former postdoctoral researcher at nanoGUNE, added.

After fabricating the metasurface, the researchers used a “state-of-the-art infrared nanoimaging technique” to see how the light waves would propagate along the material.

They placed an infrared gold nanorod on the metasurface. The nanorod acted like a stone dropped into water and concentrated incident infrared light into a tiny spot.

This, in turn, launched the waves that propagate along the metasurface. Using a scattering-type scanning near-field microscope or s-SNOM, the researchers then imaged the wavefronts.

“It was amazing to see the images. They indeed showed the concave curvature of the wavefronts that were propagating away from the gold nanorod, exactly as predicted by theory,” Rainer Hillenbrand, lead researcher of the study, said.

The study suggests that in the future, nanostructured 2D materials could become unique platforms for hyperbolic metasurface devices and circuits.

Furthermore, it demonstrates how near-field microscopy could be used to reveal rare optical phenomena in “anisotropic materials and for verifying new metasurface design principles.”

Physicists have demonstrated accelerating light beams on flat surfaces, where acceleration has caused the beams to follow curved trajectories. However, a new experiment has pushed the boundaries of what’s possible to demonstrate in a lab. For the first time in an experiment, physicists have demonstrated an accelerating light beam in curved space. Instead of traveling along a geodesic trajectory (the shortest path on a curved surface) it bends away from this trajectory due to the acceleration.

The study, published in the journal Physical Review X, “opens the doors to a new avenue of study in the field of accelerating beams. Thus far, accelerating beams were studied only in a medium with a flat geometry, such as flat free space or slab waveguides. In the current work, optical beams follow curved trajectories in a curved medium,” according to Anatoly Patsyk, a physicist from the Israeli Institute of Technology.

Completed by physicists at Israel Institute of Technology, Harvard University, and the Harvard-Smithsonian Center for Astrophysics, the success of the experiment will increase research potential for further lab-based studies of phenomena like gravitational lensing. By performing these expeirments in a lab, scientists will be able to study such phenomena which stem from Einstein’s general theory of relativity in a controlled setting.

The accelerating light beam propagates on a non-geodesic trajectory, rather than the geodesic trajectory taken by a non-accelerating beam. Credit: Patsyk et al. ©2018 American Physical Society

The team first caused a laser beam to accelerate by reflecting the beam off a spatial light modulator, which is a device used to modulate amplitude, phase, or polarize light waves. Bouncing the beam off this device imprints a specific wavefront on the beam, creating one that accelerates while keeping its shape. The team then pointed the accelerating laser along the inside of an incandescent light bulb painted in such a way that the light both scattered and was visible to the researchers.

The team observed that when moving along the inside of the bulb, the beam’s trajectory breaks apart from the geodesic line. When they compared this movement to a beam that was not accelerating, they found that when it was not accelerating, the beam would follow the line.

The research could be a starting point for future research into phenomena that fall within Einstein’s general theory of relativity. Patsyk stated that “Einstein’s equations of general relativity determine, among other issues, the evolution of electromagnetic waves in curved space. It turns out that the evolution of electromagnetic waves in curved space according to Einstein’s equations is equivalent to the propagation of electromagnetic waves in a material medium described by the electric and magnetic susceptibilities that are allowed to vary in space.”

(a) Experimental setup, (b) propagation of the green beam inside of the red shell of an incandescent light bulb, and (c) photograph of the lobes of the accelerating beam. Credit: Patsyk et al. ©2018 American Physical Society

Patsyk went on to say that this foundation gives “rise to the emulating effects such as gravitational lensing and Einstein’s rings, gravitational blue shift or red shift, which we have studied in the past, and much more.”

In other words, the techniques innovated through this experiment could help physicists more effectively study phenomena like gravitational lensing. The team is also exploring whether plasmonic beams (those that have plasma oscillations instead of light) could also be accelerated in curved space.

References: Phys, APS

Article was originally published on Futurism.

Light is ubiquitous and vital, but also incredibly strange - and it's possible we'll never exhaust the opportunities to learn more about it. Case in point: researchers at Harvard have developed a material that can generate and maintain completely new and more complex states of light. The tool uses polarization to generate structures such as swirling vortices, spirals, and corkscrews that not only help explore light's properties, but also have potential practical applications, such as high-powered imaging. Discoveries about light are still being made. It was only in 2015 that scientists took the first-ever photographof light behaving as both a particle and a wave.

And it hasn't even been that long - just 1992, 25 years ago - since light was discovered to have orbital angular momentum. This is angular momentum based on the shape of its wavefront, rather than its orientation. The new tool - a type of metasurface - uses this along with second type of angular momentum called spin angular momentum (also known as circular polarization).

Harvard's Leah Burrows writes in a statement, "Think about orbital angular momentum and circular polarization like the motion of a planet. Circular polarization is the direction in which a planet rotates on its axis while orbital momentum describes how the planet orbits the sun."

It's previously been established that a single beam of light can exhibit both types of angular momentum, and that connecting them and using polarization to control the OAM can result in beams with new and complex shapes, such as the aforementioned corkscrew. According to the researchers, until now there was a significant limit on this. Only certain polarizations could connect to certain OAMs. This is where the new tool comes in - it allows any polarization to be converted to any OAM, which means it can create spirals and corkscrews and vortices of any size.

Co-first researcher Antonio Ambrosio, Principal Scientist at Harvard Center for Nanoscale Systems said, "This is a completely new optical component. Some meta-surfaces are iterations or more efficient, more compact versions of existing optical devices but, this arbitrary spin-to-orbital conversion cannot be done with any other optical device. There is nothing in nature as well that can do this and produce these states of light."

Orbital angular momentum already has several proposed uses, such as high-speed data transfer, and encoded communications. Researchers have even figured out how to transmit the OAM of individual photons using entanglement. Other previously proposed applications include the manipulation of microscopic objects, and imaging systems. This is where Harvard's device could prove practical. The meta-surface could be used to shape optical tweezers to manipulate objects as small as atoms and molecules. Changing the polarization could change the direction of the applied force. It could also be used for high-powered imaging, because the black hole down the center of the vortex can be used to take images of features smaller than the diffraction limit, the researchers said.

Co-first researcher Noah Rubin explained, "There is interest in these beams in quantum optics and quantum information. On the more applied side, these beams could find application in free-space optical communication especially in scattering environments where this is usually difficult. Moreover, it has been recently shown that similar elements can be incorporated into lasers, directly producing these novel states of light. This may lead to unforeseen applications."

Harvard has legally protected all IP related to the project and is currently seeking commercialization opportunities. The research itself has been published in the journal Science.

Article was originally published on ScienceAlert.

For over 11 decades we have known that matter and energy are interchangeable. The development of nuclear power has shown us that matter can be converted into energy, but converting energy into matter has so far proven a lot more difficult.

The battlefield for such an achievement is at the end of the most powerful lasers ever envisioned. Currently being planned and built in a number of different countries. Three projects top the “one to watch list” of the laser world, prepared by the journal Science. They are China’s Station of Extreme Light (SEL), Russia’s Exawatt Center for Extreme Light Studies (XCELS), and the Department of Energy’s Optical Parametric Amplifier Line (OPAL).

These three lasers are planned to completely annihilate the current record for laser power, which is 5.3 million billion watts or 5.3 petawatts (PW) and obtained by Ruxin Li and colleagues at the Shanghai Superintense Ultrafast Laser Facility (SULF). Li is also behind SEL and hopes that by 2023 his team could reach the goal of a 100-PW laser.

The Russian instrument is still in the design phase of development but is more daring in its target. The researchers hope it will achieve 180 PW. Both SEL and XCELS are expected to work on the same principle. They shoot a series of pulses (four 30-PW pulses for SEL and a dozen 15-PW pulses for XCELS) and combine them into a single extra-powerful one.

Science Magreports that this approach requires extreme precision and even the smallest vibration or temperature variation can compromise the achievements of such a powerful laser pulse. For this reason, OPAL is going a different way. It is envisioned to reach 75 PW with a single pulse.

There are other facilities working on “more modest” equipment that will aim to deliver 30-PW machines and SULF itself hopes to break the 10-PW record this year. High-energy is required but it is not the only necessity to “break the vacuum” and turn photons into electrons and positrons, their antimatter counterparts.

The way that SEL is expected to do this is very interesting. The laser will hit a helium target and liberate electrons. Some of the photons from the beam will ricochet off the electrons and then collide with other photons, creating particle-antiparticle pairs.

If SEL can truly break the vacuum, it could change the way we approach particle physics. Traditional particle accelerators might be swapped for faster and cheaper laser-powered ones.

[H/T: Science Mag]