Researchers at Nagoya University develop a composite material that, by adjusting its composition and exposing it to different types of light, can mimic animals’ changes in color.
Nagoya, Japan – A range of creatures, including chameleons, octopuses, and frogs, can change color in response to changes in the environment. Some insights into the mechanisms behind this at the anatomical, cellular, and molecular levels have been obtained. However, much work is still required to obtain sufficient understanding of this phenomenon and to translate it into useful artificial applications.
As reported in the journal Small, researchers at Nagoya University’s Department of Molecular Design and Engineering developed a material containing dyes and crystals that can change the colors and patterns it displays depending on the background color used within it and its exposure to visible or ultraviolet light.
The team was inspired to develop this material by findings obtained in the skin of certain frogs, in which different layers of cells with different properties combine to enable remarkable color changes.
Chaos, often popularized as the ‘butterfly effect’, describes the irregular phenomenon of deterministic systems. Based on the unique features of sensitivity to initial conditions and unpredictability of future evolutions, chaos from laser diodes has found applications in private optical communication links, high-rate random number generations, Lidar systems, and optical computing networks. However, most chaotic light sources are operated in the near-infrared range, and hence the applications are limited to this spectral range as well.
A Chinese team of scientists, led by Professor Cheng Wang from ShanghaiTech University, China recently reported a mid-infrared hyperchaos source in Light: Science & Applications. The chaos generation relies on interband cascade lasers, one major type of laser source in the mid-infrared regime. The lasers without any external perturbation usually produce continuous-wave output. In order to trigger the chaos production, the team applied an external perturbation known as 'optical feedback’ to the lasers. Optical feedback is a technique where the laser output is reflected back to the laser cavity through a reflection mirror. The delayed light interacts nonlinearly with the laser device and generates chaos under certain operation conditions.
Ultra-precise lasers can be used for optical atomic clocks, quantum computers, power cable monitoring, and much more. But all lasers make noise, which researchers from DTU Fotonik want to minimize using machine learning.
The perfect laser does not exist. There will always be a bit of phase noise because the laser light frequency moves back and forth a little. Phase noise prevents the laser from producing light waves with the perfect steadiness that is otherwise a characteristic feature of the laser.
Most of the lasers we use on a daily basis do not need to be completely precise. For example, it is of no importance whether the frequency of the red laser light in the supermarket barcode scanners varies slightly when reading the barcodes. But for certain applications—for example in optical atomic clocks and optical measuring instruments—it is absolutely crucial that the laser is stable so that the light frequency does not vary.
One way of getting closer to an ultra-precise laser is if you can determine the phase noise. This may enable you to find a way of compensating for it, so that the result becomes a purer and more accurate laser beam.
A research team led by Dr. Byeong-dae Choi of DGIST’s Intelligent Devices and Systems Research Group has developed an electroluminescent film that is four times brighter than existing ones. The new film can improve the luminance of electroluminescent devices by 422 percent compared to conventional ones by applying retro-reflection electrodes that adapt the principle of nocturnal animal eyes.
Electroluminescent (EL) refers to an optical and electrical phenomenon in which a material emits light in response to the passage of an electric current. Electroluminescent films using phosphor powder have advantages such as excellent durability in a deformed state due to flexibility and elasticity, and high efficiency despite low cost. However, it was difficult to put into practical use due to their low brightness.
In order to increase the brightness of electroluminescent devices, the research team paid attention to the eyes of nocturnal animals with high utilization efficiency of light. The researchers used the retro-reflection characteristics that the light returns to the light source without being dispersed in the retroreflective structure of the nocturnal animal eye while it is scattered in the normal reflection structure.
For more than a century, optical coatings have been used to better reflect certain wavelengths of light from lenses and other devices or, conversely, to better transmit certain wavelengths through them. For example, the coatings on tinted eyeglasses reflect, or “block out,” harmful blue light and ultraviolet rays.
But until now, no optical coating had ever been developed that could simultaneously reflect and transmit the same wavelength, or color.
In a paper in Nature Nanotechnology, researchers at the University of Rochester and Case Western Reserve University describe a new class of optical coatings, so-called Fano Resonance Optical Coatings (FROCs), that can be used on filters to reflect and transmit colors of remarkable purity.
In addition, the coating can be made to fully reflect only a very narrow wavelength range.
Improving the sensitivity of light sensors or the efficiency of solar cells requires fine-tuning of light capturing. KAUST researchers have used complex geometry to develop tiny shell-shaped coverings that can increase the efficiency and speed of photodetectors.
Many optical-cavity designs have been investigated to seek efficiencies of light: either by trapping the electromagnetic wave or by confining light to the active region of the device to increase absorption. Most employ simple micrometer- or nanometer-scale spheres in which the light propagates around in circles on the inside of the surface, known as a whispering gallery mode.
Former KAUST scientist Der-Hsien Lien, now a postdoctoral researcher at the University of California, Berkeley, and his colleagues from China, Australia and the U.S. demonstrate that a more complex geometry comprising convex nanoscale shells improves the performance of photodetectors by increasing the speed at which they operate and enabling them to detect light from all directions.
Surface effects play an important role in the operation of some devices, explains KAUST principal investigator, Jr-Hau He. Nanomaterials offer a way to improve performance because of their high surface-to-volume ratio. “However, although nanomaterials have greater sensitivity in light detection compared to the bulk, the light–matter interactions are weaker because they are thinner,” describes He. “To improve this, we design structures for trapping light.”
Researchers have developed a new fabrication process that allows infrared (IR) glass to be combined with another glass and formed into complex miniature shapes. The technique can be used to create complex infrared optics that could make IR imaging and sensing more broadly accessible.
“Glass that transmits IR wavelengths is essential for many applications, including spectroscopy techniques used to identify various materials and substances,” said research team leader Yves Bellouard from Ecole Polytechnique Fédérale de Lausanne (EPFL) in Switzerland. “However, infrared glasses are difficult to manufacture, fragile and degrade easily in the presence of moisture.”
In the journal Optics Express, the researchers describe their new technique, which can be used to embed fragile IR glasses inside a durable silica matrix. The process can be used to create virtually any interconnected 3D shape with features measuring a micron or less. It works with a wide variety of glasses, offering a new way to fine-tune the properties of 3D optics with subtle combinations of glass.
Imagine a dim light which is insufficiently bright enough to illuminate a room. An amplifier for such a light would increase the brightness by increasing the number of photons emitted. Photonics researchers have created such a high gain optical amplifier that is compact enough to be placed on a chip. The developed amplifier, when used within an optical interconnect such as a transceiver or fiber optic network, would help to efficiently increase the power of the transmitted light before it is completely depleted through optical losses.
Besides having the potential to replace bulky, expensive amplifiers used today for the study of attosecond science and ultrafast optical information processing, the newly developed nanoscale-amplifier also provides a critical element to the optical interconnects toolkit, potentially providing regenerative amplification in short to long range interconnects. This work was a collaborative effort between researchers at the Singapore University of Technology and Design (SUTD), A*STAR Data Storage Institute and the Massachusetts Institute of Technology. Details appeared in Nature Communications on January 4th 2017.
Researchers have developed a microscope that can chemically identify individual micron-sized particles. The new approach could one day be used in airports or other high-security venues as a highly sensitive and low-cost way to rapidly screen people for microscopic amounts of potentially dangerous materials.
In the journal Optics Letters, from The Optical Society (OSA), researchers from the Massachusetts Institute of Technology’s Lincoln Laboratory, USA, demonstrated their new microscope by measuring infrared spectra of individual 3-micron spheres made of silica or acrylic. The new technique uses a simple optical setup consisting of compact components that will allow the instrument to be miniaturized into a portable device about the size of a shoebox.
“The most important advantage of our new technique is its highly sensitive, yet remarkably simple design,” said Ryan Sullenberger, associate staff at MIT Lincoln Labs and first author of the paper. “It provides new opportunities for nondestructive chemical analysis while paving the way towards ultra-sensitive and more compact instrumentation.”
They are not to eat, but this insect-inspired ordered monolayer of hollow carbon spheres may be a new, green and extremely lightweight antireflective coating that almost perfectly absorbs microwave radiation
Antireflective coatings are used to cut surface glare in everything from eyeglasses and camera lenses to solar cells, TV screens and LED devices. Now researchers from Research Institute for Nuclear Problems of Belarusian State University in Belarus and Institut Jean Lamour-Université de Lorraine in France have developed a novel, low-cost, ultra-lightweight material that could be used as an effective anti-reflective surface for microwave radiation based on the eyes of moths.
The eyes of moths are covered with a periodic, hexagonal pattern of tiny bumps smaller than the wavelength of the incident light. They act as a continuous refractive index gradient, allowing the moths to see at night and avoid nocturnal predators, like the bat. The physiology also makes the moth eye one of the most effective antireflective coatings in nature. It has already successfully been mimicked by scientists for developing high-performance antireflective coatings for visible lights – albeit coatings that are often expensive to fabricate and difficult to customize.
The new material cuts down reflections from microwaves rather than from visible light – invisible energy from a different part of the energy spectrum. Blocking microwave reflection is an important application for precise microwave measurements, and the coating may be used as a radar absorbing material in stealth technology, a technique that makes make an airplane invisible to radar, or police traffic radar that uses microwaves to measure car speed.
What happens when gold and silver just don’t cut it anymore? You turn to metallic alloys, which are what Army researchers are using to develop new designer materials with a broad range of capabilities for our Soldiers.
This is exactly what scientists Dr. David Baker and Dr. Joshua McClure from the U.S. Army Research Laboratory are doing to lighten the load and enhance the power of Soldier devices used on the battlefield.
Their research, conducted in collaboration with Prof. Marina Leite and Dr. Chen Gong at the University of Maryland and Prof. Alexandre Rocha at the Universidade Estadual Paulista in Brazil, was recently featured on the cover of the Sept. 4 issue of Advanced Optical Materials.
The research paper, “Band Structure Engineering by Alloying for Photonics,” focuses on control of the optical and plasmonic properties of gold and silver alloys by changing alloy chemical composition.
Physicists have discovered a novel kind of nanotube that generates current in the presence of light. Devices such as optical sensors and infrared imaging chips are likely applications, which could be useful in fields such as automated transport and astronomy. In future, if the effect can be magnified and the technology scaled up, it could lead to high-efficiency solar power devices.
Working with an international team of physicists, University of Tokyo Professor Yoshihiro Iwasa was exploring possible functions of a special semiconductor nanotube when he had a lightbulb moment. He took this proverbial lightbulb (which was in reality a laser) and shone it on the nanotube to discover something enlightening. Certain wavelengths and intensities of light induced a current in the sample—this is called the photovoltaic effect. There are several photovoltaic materials, but the nature and behavior of this nanotube is cause for excitement.
“Essentially our research material generates electricity like solar panels, but in a different way,” said Iwasa. “Together with Dr. Yijin Zhang from the Max Planck Institute for Solid State Research in Germany, we demonstrated for the first time nanomaterials could overcome an obstacle that will soon limit current solar technology. For now solar panels are as good as they can be, but our technology could improve upon that.”
Imagine windows that can easily transform into mirrors, or super high-speed computers that run not on electrons but light. These are just some of the potential applications that could one day emerge from optical engineering, the practice of using lasers to rapidly and temporarily change the properties of materials.
“These tools could let you transform the electronic properties of materials at the flick of a light switch,” says Caltech Professor of Physics David Hsieh. “But the technologies have been limited by the problem of the lasers creating too much heat in the materials.”
In a new study in Nature, Hsieh and his team, including lead author and graduate student Junyi Shan, report success at using lasers to dramatically sculpt the properties of materials without the production of any excess damaging heat.
“The lasers required for these experiments are very powerful so it’s hard to not heat up and damage the materials,” says Shan. “On the one hand, we want the material to be subjected to very intense laser light. On the other hand, we don’t want the material to absorb any of that light at all.” To get around this the team found a “sweet spot,” Shan says, where the frequency of the laser is fine-tuned in such a way to markedly change the material’s properties without imparting any unwanted heat.
Detecting light beyond the visible red range of our eyes is hard to do, because infrared light carries so little energy compared to ambient heat at room temperature. This obscures infrared light unless specialized detectors are chilled to very low temperatures, which is both expensive and energy-intensive.
Now researchers led by the University of Cambridge have demonstrated a new concept in detecting infrared light, showing how to convert it into visible light, which is easily detected.
In collaboration with colleagues from the UK, Spain and Belgium, the team used a single layer of molecules to absorb the mid-infrared light inside their vibrating chemical bonds. These shaking molecules can donate their energy to visible light that they encounter, ‘upconverting’ it to emissions closer to the blue end of the spectrum, which can then be detected by modern visible-light cameras.
The results, reported in the journal Science, open up new low-cost ways to sense contaminants, track cancers, check gas mixtures, and remotely sense the outer universe.
Engineers from the Jet Propulsion Laboratory and the California Institute of Technology have developed innovative flat, optical lenses that are capable of manipulating light in ways that are difficult or impossible to achieve with conventional optical devices.
The new lenses are not made of glass. Instead, silicon nanopillars are precisely arranged into a honeycomb pattern to create a “metasurface” that can control the paths and properties of passing light waves.
Applications of these devices include advanced microscopes, displays, sensors, and cameras that can be mass-produced using the same techniques used to manufacture computer microchips.
“These flat lenses will help us to make more compact and robust imaging assemblies,” said Mahmood Bagheri, a microdevices engineer at JPL and co-author of a new Nature Nanotechnology study describing the devices.
“Currently, optical systems are made one component at a time, and the components are often manually assembled,” said Andrei Faraon, an assistant professor of applied physics and materials science at Caltech, and the study’s principal investigator. “But this new technology is very similar to the one used to print semiconductor chips onto silicon wafers, so you could conceivably manufacture millions of systems such as microscopes or cameras at a time.”
An international research project led by Kazuyuki Takeda of Kyoto University and Koji Usami of the University of Tokyo has developed a new method of light detection for nuclear magnetic resonance (NMR) by up-converting NMR radio-frequency signals into optical signals.
This new detection method, appearing in the journal Optica, has the potential to provide more sensitive analysis compared with conventional NMR. Its possible utilization in higher-accuracy chemical analysis, as well as in magnetic resonance imaging (MRI) technology, are also of interest.
NMR is a branch of spectroscopy in which scientists measure the spin of an atom’s nucleus in order to determine its identity. Atomic nuclei subjected to a magnetic field induce radio-frequency signals in a detector circuit. Since different atoms cause signals at different frequencies, scientists can use this information to determine the compounds contained in a sample. The most well-known application of this is in MRI-based imagining, such as CT scans.
“NMR is a very powerful tool, but its measurements rely on amplification of electrical signals at radio-frequencies. That pulls in extra noise and limits the sensitivity of our measurements,” explains Takeda. “So we developed an experimental NMR system from scratch, which converts radio-frequency signals into optical ones.”
Nano-sized diamonds with certain defects are assetsfor people who study light.
Marko Loncar, an NSF-funded electrical engineer at Harvard School of Engineering and Applied Sciences, creates tiny structures out of diamonds and other elements to manipulate how light and matter interact on the nanoscale.
For instance, Loncar, who is part of the Nanoscale Interdisciplinary Research Team, uses diamond posts in a silver substrate as the scalable platform to enhance single photon emission by nitrogen vacancy centers in diamond.
Nitrogen vacancy centers are defects formed in diamonds that allow for the precise manipulation of absorbed photons and emitted light.
You may not want a flawed diamond on your finger, but it’s the defect that makes things like quantum computing possible.
Alkali Feldspar crystals are large in this thin section. The alkali feldspar have subhedral crystals. The quartzy matrix in some areas is intergrown at the edge of the alkali feldspar crystal faces. The muscovite crystallized in the interstitial space and have anhedral crystal faces. To differentiate between the muscovite and the biotite pleochroism comes into effect. The biotite is darker amber under PPL and muscovite is tan/light brown. Both are pleochroic under PPL.
