Remote control of heat nanosources motion and thermal-induced fluid flows by using light forces

Remote control of heat nanosources motion and thermal-induced fluid flows by using light forces
a, Multiple gold NPs (spheres of 200 nm radius) are confined by a ring-shaped laser trap (wavelength of 532 nm) and optically transported around it. These NPs rapidly assemble into a stable group of hot particles creating a confined heat source (G-NP) of temperature ~500 K. Free (not trapped) gold NPs acting as tracer particles are dragged toward the G-NP by the action of the thermal-induced water flow created around it (see Video S5 of the paper). The speed of the G-NP is controlled by the optical propulsion force which is proportional to the phase gradient strength tailored along the laser trap as displayed in b, corresponding to the transport state 1. This non-uniform propulsion force drives the G-NP reaching a maximum speed of 42 μm/s. b, Sketch of the switching of the phase gradient configuration (state 1 and 2) enabling a more sophisticated manipulation of the heat source: split and merge of the G-NP. (c), The opposite averaged propulsion forces in the split region (see state 3 at ~0 deg, shown in b) separate the NPs belonging to the original G-NP thus creating G-NP1 and G-NP2, as observed in the displayed sequence (see Video S6 of the paper). These two new heat sources are propelled by the time averaged propulsion force corresponding to state 3 in opposite directions toward the region where they finally merge into a joint G-NP again. Complex transport trajectories for G-NP delivery, for example in form of knot circuit (see Video S7 of the paper), can be created enabling spatial distribution of moving heat sources across a target network Credit: José A. Rodrigo, Mercedes Angulo and Tatiana Alieva

Today, optofluidics is one of the most representative applications of photonics for biological/chemical analysis. The ability of plasmonic structures (e.g., colloidal gold and silver nanoparticles, NPs) under illumination to release heat and induce fluid convection at the micro-scale has attracted much interest over the past two decades. Their size- and shape-dependent as well as wavelength-tunable optical and thermal properties have paved the way for relevant applications such as photothermal therapy/imaging, material processing, biosensing and thermal optofluidics to name a few. In-situ formation and motion control of plasmon-enhanced heat sources could pave the way for further harnessing of their functionalities, especially in optofluidics. However, this is a challenging multidisciplinary problem combining optics, thermodynamics and hydrodynamics.

In a recent paper published in Light Science & Applications, Professor Jose A. Rodrigo and co-workers from Complutense University of Madrid, Faculty of Physics, Department of Optics, Spain, have developed a technique for jointly controlling the formation and motion of heat sources (group of gold NPs) as well as of the associated thermal-induced fluid flows created around them. The scientists summarize the operational principle of their technique, “The technique applies a structured laser-beam trap to exert an optical propulsion force over the plasmonic NPs for their motion control, while the same laser simultaneously heats up them. Since both the shape of the laser trap and the optical propulsion forces are easily and

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Platypuses Glow Under UV Light


  • Researchers found that platypus fur actually glows under UV light
  • They made the discovery when studying the glow in another mammal species
  • The trait has been observed in many other animals but only a few mammals

What could possibly make the duck-billed platypus stranger that it already is? Researchers found that their fur also glows blue when placed under ultraviolet (UV) light.

Platypuses are some of the strangest creatures on the planet. They’re one of the very few mammals that lay eggs, they have bills and webbed feet similar to ducks’, their tails look rather like beaver tails and, apparently, they also glow an eerie shade of blue-green when exposed to UV light.

The latter was recently discovered by a team of scientists who were actually studying biofluorescence, the means by which creatures absorb and re-emit wavelengths of light, in the museum specimens of another species. According to a news release from De Gruyter, the team made the discovery while looking at flying squirrel museum specimens.

They had previously observed pink biofluorescence in flying squirrels and were confirming it in the museum specimens when they decided to also check the museum’s platypus samples for the trait.

There, they discovered that platypuses also possess biofluorescence, with their brown fur exhibiting a greenish glow under the UV light. The researchers tested another sample in different museum and also observed the glow.

“Here we document the discovery of fluorescence of the pelage of the platypus (Ornithorhynchus anatinus)—to our knowledge, the first report of biofluorescence in a monotreme mammal under UV light,” the researchers wrote in the study. 

In total, the researchers observed platypus biofluorescence in three museum samples, two of which were from the Field Museum of Natural History and the other from the University of Nebraska State Museum, the news release noted. 

“It was a mix of serendipity and curiosity that led us to shine a UV light on the platypuses at the Field Museum. But we were also interested in seeing how deep in the mammalian tree the trait of biofluorescent fur went,” study lead Paula Spaeth Anich of Northland College said in the news release. “It’s thought that monotremes branched off the marsupial-placental lineage more than 150 million years ago. So, it was intriguing to see that animals that were such distant relatives also had biofluorescent fur.”

But what could platypuses possibly have use for biofluorescence? It’s possible, the researchers say, that platypuses use this trait to interact with each other in the dark and to reduce their visibility to UV sensitive-predators.

It would be particularly useful since platypuses are most active at night and during low-light environments at dawn and dusk. However, field research is needed to confirm these hypotheses, the researchers said.

Biofluorescence has been observed in many other animals such as fishes, reptiles and amphibians, but only few mammalian species are known to posses biofluorescence, including the opossum and the flying squirrel. 

“The discovery of biofluorescence in the platypus adds a new dimension to our

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First light on a next-gen astronomical survey toward a new understanding of the cosmos

First light on a next-gen astronomical survey toward a new understanding of the cosmos
The Sloan Digital Sky Survey’s fifth generation made its first observations earlier this month. This image shows a sampling of data from those first SDSS-V data. The central sky image is a single field of SDSS-V observations. The purple circle indicates the telescope’s field-of-view on the sky, with the full Moon shown as a size comparison. SDSS-V simultaneously observes 500 targets at a time within a circle of this size. The left panel shows the optical-light spectrum of a quasar–a supermassive black hole at the center of a distant galaxy, which is surrounded by a disk of hot, glowing gas. The purple blob is an SDSS image of the light from this disk, which in this dataset spans about 1 arcsecond on the sky, or the width of a human hair as seen from about 21 meters (63 feet) away. The right panel shows the image and spectrum of a white dwarf –the left-behind core of a low-mass star (like the Sun) after the end of its life. Credit: Hector Ibarra Medel, Jon Trump, Yue Shen, Gail Zasowski, and the SDSS-V Collaboration. Central background image: unWISE/NASA/JPL-Caltech/D.Lang (Perimeter Institute).

The Sloan Digital Sky Survey’s fifth generation collected its very first observations of the cosmos at 1:47 a.m. on October 24, 2020. This groundbreaking all-sky survey will bolster our understanding of the formation and evolution of galaxies—including our own Milky Way—and the supermassive black holes that lurk at their centers.

The newly-launched SDSS-V will continue the path-breaking tradition set by the survey’s previous generations, with a focus on the ever-changing night sky and the physical processes that drive these changes, from flickers and flares of supermassive black holes to the back-and-forth shifts of stars being orbited by distant worlds. SDSS-V will provide the spectroscopic backbone needed to achieve the full science potential of satellites like NASA’s TESS, ESA’s Gaia, and the latest all-sky X-ray mission, eROSITA.

“In a year when humanity has been challenged across the globe, I am so proud of the worldwide SDSS team for demonstrating—every day—the very best of human creativity, ingenuity, improvisation, and resilience. It has been a challenging period for the team, but I’m happy to say that the pandemic may have slowed us, but it has not stopped us,” said SDSS-V Director Juna Kollmeier.

As an international consortium, SDSS has always relied heavily on phone and digital communication. But adapting to exclusively virtual communication tactics was a challenge, as was tracking global supply chains and laboratory availability at various university partners while they shifted in and out of lockdown during the final ramp-up to the survey’s start. Particularly inspiring were the project’s expert observing staff, who worked in even-greater-than-usual isolation to shut down, and then reopen, operations at the survey’s mountain-top observatories.

Funded primarily by member institutions, along with grants from the Alfred P. Sloan Foundation, the U.S. National Science Foundation, and the Heising-Simons Foundation, SDSS-V will focus on three primary areas of investigation, each exploring different aspects of the cosmos using different spectroscopic tools. Together

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GRETA, a 3-D gamma-ray detector, gets green light to move forward

GRETA, a 3D gamma-ray detector, gets green light to move forward
This set of renderings shows the completed GRETA array (top and bottom left) and half of the completed array (right). The detector is designed to open up, with each half sliding on tracks. Samples can be placed at the center of the spherical array. The completed array will contain 120 high-purity germanium crystals. Credit: GRETA collaboration

The effort to construct GRETA (Gamma-Ray Energy Tracking Array), a cutting-edge spherical array of high-purity germanium crystals that will measure gamma-ray signals to reveal new details about the structure and inner workings of atomic nuclei, has received key approvals needed to proceed toward full build-out.

GRETA, which will also provide new insight about the nature of matter and how stars create elements, is expected to reach the first phase of completion in 2023, and to achieve final completion in 2025. It builds on the existing GRETINA (Gamma-Ray Energy Tracking In-beam Nuclear Array) instrument, completed in 2011, which features fewer gamma-ray-detecting crystals. Gamma rays are very energetic, penetrating forms of light that are emitted as unstable atomic nuclei decay into more stable nuclei.

The U.S. Department of Energy’s Lawrence Berkeley National Laboratory (Berkeley Lab) has had a leadership role in both GRETINA and GRETA, and Berkeley Lab nuclear physicists and engineers are working with teams at Argonne and Oak Ridge national laboratories, and Michigan State University, in the development of GRETA.

On Wednesday, Oct. 7, 2020, DOE officials approved key milestones for the GRETA project, including the scope of work and its schedule, and the final construction engineering plans that will guide the project through to completion. The formal approval steps are known as Critical Decision 2 and Critical Decision 3 (CD-2 and CD-3).

“The approvals were a major achievement for the project and the team. It marks the successful completion of the final design, and demonstrates we are ready to build the array,” said Paul Fallon, GRETA project director and a senior staff scientist in Berkeley Lab’s Nuclear Science Division. A key next step is to fabricate the complex, meter-wide aluminum sphere that will house the detectors.

New user facility will put GRETA to work

GRETINA, and later GRETA, will be installed at Michigan State University’s Facility for Rare Isotope Beams (FRIB), when that facility begins operations in 2022. On Sept. 29, FRIB was officially designated as the newest member of the DOE Office of Science’s user facilities. There are now 28 of these user facilities, which are accessible to scientists from across the country and around the world. Already, an estimated 1,400 scientific users are lined up to participate in nuclear physics experiments at FRIB once that facility starts up in 2022. Still under construction, FRIB is about 94% complete.

GRETINA is equipped with 12 detector modules and 48 detector crystals, and GRETA will add 18 more detector modules, for a total of 30 modules and 120 crystals. About 18-20 detector modules are expected to be installed in GRETA before the end of 2024, with the final modules installed in 2025.

When the

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Best work light for mechanics in 2020

I have quite a few lights hanging in my garage, but no matter how bright they are, they never seem to shine exactly where I need them to. Whether I’m reaching down in an engine bay or hunched inside a fender liner, a little extra illumination can make a miserable car repair job… well, a little less miserable anyway.

There are plenty of options out there that address a lot of different needs. What follows are my top 10 picks for the best work light for mechanics.

Read more: Best headlight restoration kits in 2020   

Harbor Freight

The shop light I found myself reaching for most often is actually one of the cheapest here, this $35 folding unit from Braun (Harbor Freight’s house brand). While its length makes it difficult to throw in a toolbox, the strong magnet on the base means you can just pop it onto any metal surface — like, say, the side of your toolbox. The LED light bar throws off plenty of light output for bigger jobs, while the LEDs on the tip meant I could easily inspect down in the fuel tank of my tractor. I got 2 hours on a charge with the LED work light bar on full blast, so it’s maybe not the best work light for mechanics who need it for longer jobs. But it’s a great, affordable rechargeable LED work light choice for most tasks. And, if you catch it at the right time, you can get it for $27 — before the ubiquitous HF coupon!

Harbor Freight

If you’re looking to spend a little more on a portable rechargeable work light, the $50 Braun 3-In-1 Quick Connect Light Kit comes with replaceable attachments, giving you a more powerful flashlight and a snake light as well. It’s a great portable work light kit, but that means you’ll need to also keep the case and all accessories around. I much prefer the cheaper, integrated lighting option.

Harbor Freight

Another win for Harbor Freight here, with the Ultra Bright portable LED work light and flashlight. I’m going to go out on a limb and say that if you’ve ever visited a Harbor Freight, you probably walked out with one of these portable LED flashlight and work light units for free. And, if you’re a frequent shopper, you probably have a half-dozen scattered around your house and garage. Even at the full price of $4, it’s hard to ignore the value here. Whether you want focused or broad LED light, an underhood light, or a powerful flashlight, this will deliver. My only complaint is that the AAA batteries inside are too difficult to replace and the whole thing has a tendency to fly into pieces when dropped on a concrete floor, as mine have been. Repeatedly.

Black Diamond

When I asked for work light suggestions, a number of you indicated you prefer to use headlamps when working on your cars, and I definitely can see why. My choice is the $50

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How Fireflies’ Dramatic Light Show Might Spark Advances in Robot Communication | Science

On an early June evening, physicist Raphael Sarfati breathed hard as he lumbered up a dense forest trail in Great Smoky Mountains National Park. The French-born scientist lugged more than 40 pounds of gear, including a tent, generators, butterfly nets and two GoPro 360-degree cameras vital to photographing his subject. Sarfati, a postdoctoral associate at the University of Colorado, Boulder, and his advisor, assistant professor of computer science Orit Peleg, trekked into the forest to film how synchronous fireflies conduct their impressive light display, a show that lasts for just 10-to-15 days each year and only for a few hours each night. Unlike many firefly species that flash in individualized patterns for months every summer, these special fireflies display in a specific, collective pattern that the scientists wanted to track.

With their tent and cameras set up and dusk descending, the sporadic blinking of individual fireflies harmonized into synchronous flashing. “They are everywhere around you. You can’t even count how many there are, all flashing at the same time for a few seconds and then they all stop at the same time as well. It’s dark and then it picks it up again,” Sarfati says. “It’s really astonishing.”

“How do thousands or tens of thousands of individuals all know how to flash at the same time when they can only see a fraction of the insects around them?” Peleg marvels. “There are a lot of interesting aspects of firefly communication, and we’re hoping to shed light on them.”

Now, in a study published in September in the Journal of the Royal Society Interface, Sarfati and Peleg have shown how to recreate the fireflies’ flashes and flight trajectories three-dimensionally. Their findings provide clues into how simple insects with limited cognitive functionality can accomplish complicated, synchronous tasks. By demonstrating how fireflies begin to synchronize, their research might inspire communication and coordination methods in swarm robotics technology. It will also serve as a resource for firefly conservation efforts by providing a more accurate way to monitor their populations.

Sarfati and Peleg had come to Great Smoky Mountains National Park to study Photinus carolinus. The scientists first set up their 360-degree cameras in the forest to capture the insects’ behavior in their natural, unperturbed environment. Male fireflies, thick in the air, flew around and flashed in unison to attract the relatively stationary females waiting on the ground below. Standing in the cloud of Morse-code-like intervals of light, the researchers could see a lone male flashing here or there along with his brethren. However, their cameras tracked what their naked eye could not: trajectories of exactly where individual fireflies were in three-dimensional space when they flashed. By tracking the flashes, the team was able to recreate the flight patterns of each insect caught on camera.

Sarfati and Peleg next set up the tent as their control environment and added dozens of male fireflies to the space—enough to elicit the same swarm behavior found in their natural environment. Then, with cameras rolling inside the

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Light on efficiency loss in organic solar cells

Light on efficiency loss in organic solar cells
Using a complex laser setup, the team discovered that contrary to recent reports, substantial ionization energy offsets were needed to generate charges. Credit: © 2020 KAUST; Anastasia Serin

Insight into energy losses that affect the conversion of light into electricity could help enhance organic solar cell efficiencies. A KAUST-led team of organic chemists, materials engineers, spectroscopists and theoretical physicists from six research groups has extensively evaluated efficiency-limiting processes in organic photovoltaic systems.

To harvest light, cutting-edge organic solar cells rely on bulk heterojunctions, blends of light-responsive electron donor and acceptor materials. When light strikes the heterojunction, the resulting excited states are pairs of electrons and positively charged holes that need to be separated to make electric current. During charge separation, the donor gives electrons to the acceptor, and the acceptor transfers holes to the donor. Therefore, the efficiency of the solar cells depends on two key factors: the electron affinity offset between these materials, which corresponds to the ability of the acceptor to gain an electron and drives electron transfer; and the ionization energy offset, which represents the propensity of the donor to release an electron, facilitating hole transfer.

Nonfullerene acceptors (NFAs) have recently yielded solar cells with conversion efficiencies nearing 20 percent, outperforming fullerene-based acceptors that had previously dominated. “Key to these record efficiencies is the design and synthesis of materials that combine efficient charge generation with minimal energy losses,” explains team leader Frédéric Laquai. “However, the precise role of the energy offsets and their related processes is unclear, which has stalled the development of design rules for NFA-based systems” he adds.

To address this, the multidisciplinary team devised an approach to monitor the photophysical processes that influence charge generation in 23 different NFA-based systems. “With our collaborator, Denis Andrienko from the Max Planck Institute for Polymer Research in Germany, we developed a concise model that enabled us to correlate our experimental observations to physical parameters and chemical structures,” says research scientist, Julien Gorenflot.

The researchers discovered that, contrary to recent reports, substantial ionization energy offsets were needed to generate charges. In contrast, electron affinity offsets failed to induce charge separation regardless of their magnitude. These unexpected findings result from a process known as Förster resonance energy transfer, which appears to compete with electron transfer. Postdoc Catherine De Castro explains that “this is an immediate consequence of the design principle of the blends, where donor and acceptor present overlapping emission and absorption, which facilitates energy transfer.”

The team plans to design new materials combining enhanced charge generation efficiencies with lower energy losses. “This will help reduce the efficiency gap to other emerging photovoltaic technologies and bring organic photovoltaics closer to maturity and application,” Gorenflot says.

The study is published in Nature Materials.

Benchmarks to better catch the sun

More information:
Intrinsic efficiency limits in low-bandgap non-fullerene acceptor organic solar cells, Nature Materials, DOI: 10.1038/s41563-020-00835-x ,
Provided by
King Abdullah University of Science and Technology

Light on efficiency loss in organic solar cells (2020, October

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New study details atmosphere on ‘hot Neptune’ 260 light years away that ‘shouldn’t exist’

New study details atmosphere on 'hot Neptune' 260 light years away that 'shouldn't exist'
This artist’s impression shows the LTT9779 system approximately to scale, with the hot Neptune-sized planet at left and its bright, nearby star at right. The trail of material streaming off of the planet is hypothetical but likely, based on the intense irradiation of this planet. Credit: Ethen Schmidt | University of Kansas

A team led by an astronomer from the University of Kansas has crunched data from NASA’s TESS and Spitzer space telescopes to portray for the first time the atmosphere of a highly unusual kind of exoplanet dubbed a “hot Neptune.”

The findings concerning the recently found planet LTT 9779b were published today in Astrophysical Journal Letters. The paper details the very first spectral atmospheric characterization of any planet discovered by TESS, the first global temperature map of any TESS planet with an atmosphere and a hot Neptune whose emission spectrum is fundamentally different from the many larger “hot Jupiters” previously studied.

“For the first time, we measured the light coming from this planet that shouldn’t exist,” said Ian Crossfield, assistant professor of physics & astronomy at KU and lead author of the paper. “This planet is so intensely irradiated by its star that its temperature is over 3,000 degrees Fahrenheit and its atmosphere could have evaporated entirely. Yet, our Spitzer observations show us its atmosphere via the infrared light the planet emits.”

While LTT 9779b is extraordinary, one thing is certain: People probably wouldn’t like it there very much.

“This planet doesn’t have a solid surface, and it’s much hotter even than Mercury in our solar system—not only would lead melt in the atmosphere of this planet, but so would platinum, chromium and stainless steel,” Crossfield said. “A year on this planet is less than 24 hours—that’s how quickly it’s whipping around its star. It’s a pretty extreme system.”

Hot Neptune LTT 9779b was discovered just last year, becoming one of the first Neptune-sized planets discovered by NASA’s all-sky TESS planet-hunting mission. Crossfield and his co-authors used a technique called “phase curve” analysis to parse the exoplanet’s atmospheric makeup.

“We measure how much infrared light was being emitted by the planet as it rotates 360 degrees on its axis,” he said. “Infrared light tells you the temperature of something and where the hotter and cooler parts of this planet are—on Earth, it’s not hottest at noon; it’s hottest a couple of hours into the afternoon. But on this planet, it’s actually hottest just about at noon. We see most of the infrared light coming from the part of the planet when its star is straight overhead and a lot less from other parts of the planet.”

“For the first time, we measured the light coming from this planet that shouldn’t exist,” said Ian Crossfield, assistant professor of physics & astronomy at KU and lead author of the paper. “This planet is so intensely irradiated by its star that its temperature is over 3,000 degrees Fahrenheit and its atmosphere could have evaporated entirely. Yet, our Spitzer observations show
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New investigation of South African rock shelter sheds light into Middle and Later modern human behavior

New investigation of South African rock shelter sheds light into Middle and Later modern human bahaviour
Credit: Leiden University

In the 1980s, the Umhlatuzana rock shelter in Kwa-Zulu Natal, South Africa, was excavated. Results from this excavation led to an understanding when the Later Stone Age started in this area. This archeological period is often associated with the structural presence of modern human behavior. Now a team of archeologists has published on this site employing new methods of analysis and reaching new conclusions. We spoke with its first author, Irini Sifogeorgaki.


There are many rock shelter sites in this region of South Africa. The Umhlatuzana one, however, is remarkable. “This site has both Later Stone Age and Middle Stone Age artifacts,” Irini Sifogeorgaki explains. “While it is common for sites to feature finds from one of the periods, a combination is rare. This site contains important information regarding the transition between both periods.” The transition between Middle and Later Stone Age is marked by a change in lithic technology, possibly to adapt subsistence strategies due to different environmental conditions. The Middle Stone Age in South Africa is often related with the first signs of modern human behavior. “The site features a lot of ochre, for example, which can be an indication of people creating art, which is associated with modern humans.”


While the site had already been excavated in 1985, its stratigraphy remained poorly understood, and the general academic consensus did not take the findings seriously. For this reason, it was about time to return to the rock shelter and reinvestigate the site with new analytical technologies. “We employed a whole range of types of analyses: sedimentological, geochemical, mineralogical, phytolith, as well as isotope analyses. We also performed cluster analysis on the 3-dimentional projection of the excavated finds in the computer.” Sifogeorgakis elaborates. “Combining the data of all these analytical methods, we came to an updated stratigraphy of the site.”

And this stratigraphy is important, for it indicates the sequence of deposition and former ground levels. “We grouped the whole sequence into two groups. The upper part is the most recent, the Holocene group. Unfortunately, the dating of the site is not really clear yet, this remains under investigation. The lower part is the Pleistocene group and it features very different characteristics.”

Credit: Leiden University

Horizontal layers

But what does that mean exactly? “It means that there is a much better preservation of stratigraphic layers on the upper group than in the lower group. Why is not clear yet, but it was nice to confirm this also through analysis.” And another interesting detail came up. “After the excavation we divided the stratigraphy in high find density units and low find density units of finds. This was something that was not done before. The result of this was that we discovered that layers are, and were, horizontal. This is one of the most important finds of the site.”

Bigger picture

New investigation of South African rock shelter sheds light into Middle and Later modern human bahaviour
Credit: Leiden University

A time-constant horizontal layer indicates a space where people could have lived, which has not been disturbed over the millennia. “The problem

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A trillion turns of light nets terahertz polarized bytes

A trillion turns of light nets terahertz polarized bytes
A pictorial schematic depicts the structure and action of a nanopatterned plasmonic metasurface that modulates polarized light at terahertz frequencies. An ultrashort laser pulse (green) excites cross-shaped plasmonic structures, which rotate the polarity of a second light pulse (white) that arrives less one picosecond after the first. Credit: A. Assié

U.S. and Italian engineers have demonstrated the first nanophotonic platform capable of manipulating polarized light 1 trillion times per second.

“Polarized light can be used to encode bits of information, and we’ve shown it’s possible to modulate such light at terahertz frequencies,” said Rice University’s Alessandro Alabastri, co-corresponding author of a study published this week in Nature Photonics.

“This could potentially be used in wireless communications,” said Alabastri, an assistant professor of electrical and computer engineering in Rice’s Brown School of Engineering. “The higher the operating frequency of a signal, the faster it can transmit data. One terahertz equals 1,000 gigahertz, which is about 25 times higher than the operating frequencies of commercially available optical polarization switches.”

The research was a collaboration between experimental and theoretical teams at Rice, the Polytechnic University of Milan (Politecnico) and the Italian Institute of Technology (IIT) in Genoa. This collaboration started in the summer of 2017, when study co-first author Andrea Schirato was a visiting scholar in the Rice lab of physicist and co-author Peter Nordlander. Schirato is a Politecnico-IIT joint graduate student under the supervision of co-corresponding author Giuseppe Della Valle of Politecnico and co-author Remo Proietti Zaccaria of IIT.

Each of the researchers work in nanophotonics, a fast-growing field that uses ultrasmall, engineered structures to manipulate light. Their idea for ultrafast polarization control was to capitalize on tiny, fleeting variations in the generation of high-energy electrons in a plasmonic metasurface.

A trillion turns of light nets terahertz polarized bytes
A scanning electron microscope image of the nanopatterned plasmonic metasurface that engineers from Rice University, the Polytechnic University of Milan and the Italian Institute of Technology created to modulate polarized light at terahertz frequencies. Credit: Andrea Toma/IIT

Metasurfaces are ultrathin films or sheets that contain embedded nanoparticles that interact with light as it passes through the film. By varying the size, shape and makeup of the embedded nanoparticles and by arranging them in precise two-dimensional geometric patterns, engineers can craft metasurfaces that split or redirect specific wavelengths of light with precision.

“One thing that differentiates this from other approaches is our reliance on an intrinsically ultrafast broadband mechanism that’s taking place in the plasmonic nanoparticles,” Alabastri said.

The Rice-Politecnico-IIT team designed a metasurface that contained rows of cross-shaped gold nanoparticles. Each plasmonic cross was about 100 nanometers wide and resonated with a specific frequency of light that gave rise to an enhanced localized electromagnetic field. Thanks to this plasmonic effect, the team’s metasurface was a platform for generating high-energy electrons.

“When one laser light pulse hits a plasmonic nanoparticle, it excites the free electrons within it, raising some to high-energy levels that are out of equilibrium,” Schirato said. “That means the electrons are ‘uncomfortable’ and eager to return to a more

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