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Scooped by Dr. Stefan Gruenwald!

Helically twisted photonic crystal fibers show surprising features

Helically twisted photonic crystal fibers show surprising features | Amazing Science |

Photonic crystal fibers (PCF) are strands of glass, not much thicker than a human hair, with a lattice of hollow channels running along the fiber. If they are continuously twisted in their production, they resemble a multi-helix. Twisted PCFs show some amazing features, from circular birefringence to conservation of the angular momentum. The biggest surprise, however, is the robust light guidance itself, with no visible fiber core. The basis for this are forces which, like gravitation, are based on the curvature of space.

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Bubble-printed patterning of quantum dots on plasmonic substrates

Bubble-printed patterning of quantum dots on plasmonic substrates | Amazing Science |

The use of quantum dots (QDs) in practical applications relies on the ability to precisely pattern QDs on substrates with desired optical properties. Typical direct-write printing techniques such as inkjet and gravure printing are limited in resolution (micron-scale), structural complexity, and require significant post-processing time.In new work, researchers at the University of Texas at Austin use laser-induced bubble printing to pattern CdSe/CdS QDs on plasmonic substrates with submicron resolution (<700nm line width), high throughput (∼10E4 µm/s) and strong QD-substrate adhesion.Not only is the bubble-mediated immobilization at the submicron scale stable, but the submicron-sized bubble's stability can be maintained over a large area.


This technique is also compatible with flexible substrates and can be further integrated with smartphone to realize haptic integration. Finally, the emission characteristics of the QDs in terms of the emission wavelength and lifetime can be modified in real-time to achieve site-sensitive emission.The team, led by Yuebing Zheng, Assistant Professor of Mechanical Engineering and Materials Science & Engineering has been published in ACS Applied Materials & Interfaces ("High-Resolution Bubble Printing of Quantum Dots").

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Many ways to spin a photon: Half-quantization of a total optical angular momentum

Many ways to spin a photon: Half-quantization of a total optical angular momentum | Amazing Science |

The angular momentum of light plays an important role in many areas, from optical trapping to quantum information. In the usual three-dimensional setting, the angular momentum quantum numbers of the photon are integers, in units of the Planck constantħ. A group of scientists now show that, in reduced dimensions, photons can have a half-integer total angular momentum. They identify a new form of total angular momentum, carried by beams of light, comprising an unequal mixture of spin and orbital contributions. The scientists demonstrate the half-integer quantization of this total angular momentum using noise measurements. They conclude that for light, as is known for electrons, reduced dimensionality allows new forms of quantization.

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Researchers generate proton beams using a combination of nanoparticles and laser light

Researchers generate proton beams using a combination of nanoparticles and laser light | Amazing Science |

Light, when strongly concentrated, is enormously powerful. Now, a team of physicists led by Professor Jörg Schreiber from the Institute of Experimental Physics – Medical Physics, which is part of the Munich-Centre for Advanced Photonics (MAP), a Cluster of Excellence at LMU Munich, has used this energy source with explosive effect. The researchers focus high-power laser light onto beads of plastic just a few micrometers in size. The concentrated energy blows the nanoparticles apart, releasing radiation made up of positively charged atoms (protons). Such proton beams could be used in future for treating tumors, and in advanced imaging techniques. Their findings appear in the journal Physical Review E.

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Single-photon source is efficient and indistinguishable

Single-photon source is efficient and indistinguishable | Amazing Science |

New device could find use in "boson-sampling" quantum computers.


A source of single photons that meets three important criteria for use in quantum-information systems has been unveiled in China by an international team of physicists. Based on a quantum dot, the device is an efficient source of photons that emerge as solo particles that are indistinguishable from each other. The researchers are now trying to use the source to create a quantum computer based on "boson sampling".


Devices that emit one – and only one – photon on demand play a central role in light-based quantum-information systems. Each photon must also be emitted in the same quantum state, which makes each photon indistinguishable from all the others. This is important because the quantum state of the photon is used to carry a quantum bit (qubit) of information.


Quantum dots are tiny pieces of semiconductor that show great promise as single-photon sources. When a laser pulse is fired at a quantum dot, an electron is excited between two distinct energy levels. The excited state then decays to create a single photon with a very specific energy. However, this process can involve other electron excitations that result in the emission of photons with a wide range of energies – photons that are therefore not indistinguishable.


This problem can be solved by exciting the quantum dot with a pulse of light at the same energy as the emitted photon. This is called resonance fluorescence, and has been used to create devices that are very good at producing indistinguishable single photons. However, this process is inefficient, and only produces a photon about 6% of the time.


Now, Chaoyang Lu, Jian-Wei Pan and colleagues at the University of Science and Technology of China have joined forces with researchers in Denmark, Germany and the UK to create a resonance-fluorescence-based source that emits a photon 66% of the time when it is prompted by a laser pulse. Of these photons, 99.1% are solo and 98.5% are in indistinguishable quantum states – with both figures of merit being suitable for applications in quantum-information systems.

Lu told that nearly all of the laser pulses that strike the source produce a photon, but about 34% of these photons are unable to escape the device. The device was operated at a laser-pulse frequency of 81 MHz and a pulse power of 24 nW, which is a much lower power requirement than other quantum-dot-based sources.


The factor-of-ten improvement in efficiency was achieved by sandwiching a quantum dot in the centre of a "micropillar" created by stacking 40 disc-like layers (see figure). Each layer is a "distributed Bragg reflector", which is a pair of mirrors that together have a thickness of one quarter the wavelength of the emitted photons. The micropillar is about 2.5 μm in diameter and about 10 μm tall, and it allowed the team to harness the "Purcell effect", whereby the rate of fluorescence is increased significantly when the emitter is placed in a resonant cavity.

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Technique for “phase locking” arrays of tiny lasers could lead to terahertz security scanners

Technique for “phase locking” arrays of tiny lasers could lead to terahertz security scanners | Amazing Science |
A new technique for phase-locking arrays of terahertz lasers using mutual admittance borrows techniques from antenna engineering.


Terahertz radiation — the band of electromagnetic radiation between microwaves and visible light — has promising applications in security and medical diagnostics, but such devices will require the development of compact, low-power, high-quality terahertz lasers.


In a recent issue of Nature Photonics, researchers at MIT and Sandia National Laboratories describe a new way to build terahertz lasers that could significantly reduce their power consumption and size, while also enabling them to emit tighter beams, a crucial requirement for most practical applications.

The work also represents a fundamentally new approach to laser design, which could have ramifications for visible-light lasers as well.


The researchers’ device is an array of 37 microfabricated lasers on a single chip. Its power requirements are so low because the radiation emitted by all of the lasers is “phase locked,” meaning that the troughs and crests of its waves are perfectly aligned. The device represents a fundamentally new way to phase-lock arrays of lasers.


In their paper, the researchers identified four previous phase-locking techniques, but all have drawbacks at the microscale. Some require positioning photonic components so closely together that they’d be difficult to manufacture. Others require additional off-chip photonic components that would have to be precisely positioned relative to the lasers. Hu and his colleagues’ arrays, by contrast, are monolithic, meaning they’re etched entirely from a single block of material.


“This whole work is inspired by antenna engineering technology,” says Qing Hu, a distinguished professor of electrical engineering and computer science at MIT, whose group led the new work. “We’re working on lasers, and usually people compartmentalize that as photonics. And microwave engineering is really a different community, and they have a very different mindset. We really were inspired by microwave-engineer technology in a very thoughtful way and achieved something that is totally conceptually new.”

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Twisted light with high orbital angular momentum travels slower than the speed of light

Twisted light with high orbital angular momentum travels slower than the speed of light | Amazing Science |

That the speed of light in free space c is constant has been a pillar of modern physics since the derivation of Maxwell and in Einstein’s postulate in special relativity.


That the speed of light in free space c is constant has been a pillar of modern physics since the derivation of Maxwell and in Einstein’s postulate in special relativity. This has been a basic assumption in light’s various applications. However, a physical beam of light has a finite extent such that even in free space it is by nature dispersive. The field confinement changes its wavevector, hence, altering the light’s group velocity vg. Here, a group of scientists now reports the subluminal vg and consequently the dispersion in free space of Laguerre-Gauss (LG) beam, a beam known to carry orbital angular momentum. The vg of LG beam, calculated in the paraxial regime, is observed to be inversely proportional to the beam’s divergence θ0, the orbital order ℓ and the radial order p. LG beams of higher orders travel relatively slower than that of lower orders. As a consequence, LG beams of different orders separate in the temporal domain along propagation. This is an added effect to the dispersion due to field confinement.


These results are useful for treating information embedded in LG beams from astronomical sources and/or data transmission in free space.




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Two-beam super-resolution lithography to make 3D photonic 'gyroid' nanostructures

Two-beam super-resolution lithography to make 3D photonic 'gyroid' nanostructures | Amazing Science |

"A team of researchers with Swinburne University of Technology in Australia has found a way to use two-beam super-resolution lithography to create 3D photonic "gyroid" nanostructures—similar to those found in butterfly wings. In their paper published in the journal Science Advances, the team describes their technique and some applications to which it might be applied.

Scientists have known for some time that butterfly wings have "gyroid" nanostructures in them (arranged in grid patterns), that serve the butterflies by manipulating light in useful ways. In addition to their photonic properties, the structures, which are made of intertwining curved surfaces, were also found to be very strong for their size, which has caused scientists to see if they might find a way to create them artificially. Up till now, such efforts have left a lot to be desired—most do not have a high enough resolution or are too fragile. In this new effort, the researchers report that rather than rely on traditional methods, such as two-photon polymerization, the team went with optical two-beam super-resolution lithography—they compare it to direct laser writing techniques, noting that it has two major advantages over other techniques used in the past. The first is that it offers much better resolution and the second is that the resulting structure has more mechanical strength."

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Twisted light could dramatically boost internet speeds - by 6 orders of magnitude

Twisted light could dramatically boost internet speeds - by 6 orders of magnitude | Amazing Science |

Fiber optics allow for the communication of data at the speed of light. But the amount of data that can be sent along any optic fiber is limited by how much information you can encode into the light wave travelling through it. Currently, optic fiber technology uses several different properties of light to encode information, including brightness, color, polarization and direction of propagation. But if we want to cram even more information through optic fiber, we need to use other features of light to encode more information, without disrupting the currently used properties. Such a feature could help boost the bandwidth of optic fiber technology, including our internet speed.


If the light wave travelling through the optic fiber is twisted helically – like a spring – then it has an angular momentum, which is a measure of its momentum when it rotates around a point. But there was a major problem with using angular momentum to decode the information from the optic fiber in the past. We needed a material with tiny nanoscale helical structures that could detect the twisted light when present.

A research team now published in Science, how the angular momentum of light at a nanoscale can be controlled by using an integrated photonic chip. So for the first time, we have a chip with a series of elaborate nano-apertures and nano-grooves that allow for the on-chip manipulation of twisted light.


The helical design of these tiny apertures and grooves removes the need for any other bulky interference-based optics to detect the angular momentum signals. So if you send an optical data signal to a photonic chip, which is a microchip that uses light instead of electrons, then it is important to know where the data is going, otherwise information will be lost. Using this type of a nanophotonic chip, the researchers could precisely guide angular momentum data signals without losing the information they carry. What’s more, the angular momentum information of many different signals can be processed at the same time through the chip. This means we can potentially achieve an ultra-wide bandwidth, with six orders of magnitude of increased data access compared to current technology.

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Triple entanglement in three dimensions: Three "twisted" photons entangled

Triple entanglement in three dimensions: Three "twisted" photons entangled | Amazing Science |

Researchers at the Institute of Quantum Optics and Quantum Information (IQOQI), the University of Vienna, and the Universitat Autonoma de Barcelona have achieved a new milestone in quantum physics: they were able to entangle three particles of light in a high-dimensional quantum property related to the "twist" of their wavefront structure. Just like Schrödinger's famous cat that is simultaneously dead and alive, all previous demonstrations of multi-particle entanglement have been with quantum objects in two discrete levels, or dimensions. The twisted photons used in the Vienna experiment have no such limit to their dimensionality, and can simultaneously exist in three or more quantum states. The three-photon entangled state created by the Vienna group breaks this previous record of dimensionality, and brings to light a new form of asymmetric entanglement that has not been observed before. The results from their experiment appear in the journal Nature Photonics.

Entanglement is a counterintuitive property of quantum physics that has long puzzled scientists and philosophers alike. Entangled quanta of light seem to exert an influence on each other, irrespective of how much distance is between them. Consider for example a metaphorical quantum ice dancer, who has the uncanny ability to pirouette both clockwise and counter-clockwise simultaneously. A pair of entangled ice-dancers whirling away from each other would then have perfectly correlated directions of rotation: If the first dancer twirls clockwise then so does her partner, even if skating in ice rinks on two different continents. "The entangled photons in our experiment can be illustrated by not two, but three such ice dancers, dancing a perfectly synchronized quantum mechanical ballet," explains Mehul Malik, the first author of the paper. "Their dance is also a bit more complex, with two of the dancers performing yet another correlated movement in addition to pirouetting. This type of asymmetric quantum entanglement has been predicted before on paper, but we are the first to actually create it in the lab."

The scientists created their three-photon entangled state by using yet another quantum mechanical trick: they combined two pairs of high-dimensionally entangled photons in such a manner that it became impossible to ascertain where a particular photon came from. Besides serving as a test bed for studying many fundamental concepts in quantum mechanics, multi-photon entangled states such as these have applications ranging from quantum computing to quantum encryption. Along these lines, the authors of this study have developed a new type of quantum cryptographic protocol using their state that allows different layers of information to be shared asymmetrically among multiple parties with unconditional security. "The experiment opens the door for a future quantum Internet with more than two partners and it allows them to communicate more than one bit per photon," says Anton Zeilinger. Many technical challenges remain before such a quantum communication protocol becomes a practical reality. However, given the rapid progress in quantum technologies today, it is only a matter of time before this type of entanglement finds a place in the quantum networks of the future.

Publication in "Nature Photonics": Multi-Photon Entanglement in High Dimensions: Mehul Malik, Manuel Erhard, Marcus Huber, Mario Krenn, Robert Fickler, Anton Zeilinger. Nature Photonics, 2016

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Processor With Photonic Interconnects Built

Processor With Photonic Interconnects Built | Amazing Science |

Chip designers would love to use light beams rather than copper wires to move data between microprocessors. Such optical interconnects would overcome the bandwidth bottleneck inherent in the wires and take full advantage of the leaps in processor speed, but marrying two very different technologies—electronics and photonics—has been a high hurdle to overcome.

Now a group of researchers has proposed a way to build transistors and optics on the same chip, doing so for the first time without a major overhaul of the chip-making process. And they used it to build an IC containing 70 million transistors and 850 photonic components, which together provide all the logic, memory, and interconnection functions a processor needs.

Engineers at MIT, the University of California, Berkeley, and the University of Colorado, Boulder founded a start-up to commercialize what they call their “zero-change” approach to chip-making. It relies on the standard CMOS processes used to make today’s computer chips—specifically a high-performance process for the so-called 45-nanometer node, which debuted in 2007. “We didn’t make any changes to the process,” says Chen Sun, lead author of a paper on the process that appears in this week’s issue of Nature.

They started with a silicon substrate, then added a 200-nm thick layer of silicon-oxide, which acts as an insulator. Over that is the active layer—100 nm of crystalline silicon—plus a 100-nm layer of nitrides and a dielectric coating. The crystalline silicon includes a small amount of germanium to produce strain on the silicon and speed up the circuits. 

“We are able to use those existing layers to make our processors,” Sun says. The processor they constructed was a dual-core RISC-V architecture—an open instruction set architecture originally developed at Berkeley. It also included 1 megabyte of SRAM memory.

One key component to the photonics portion of the chip is a micro-ring resonator, a loop 10 micrometers across that’s coupled to a waveguide. They dope the structure with the same elements used to make p-n junctions in the transistors, and that action creates a notch filter, which passes all incoming light but a single wavelength. Putting a negative voltage across the junction pushes the charge carriers out of the ring, while a positive voltage returns them, creating a modulator that imprints digital signals on the light beam.

The micro-ring also lets the photodetector work. Normally, a photodetector made of the SiGe in the chip would have to be many millimeters to a centimeter long in order to have a chance of absorbing enough photons to actually detect the light. With the micro-ring resonator, the light passes through so many times that the SiGe can absorb it.

Micro-ring resonators have existed for a while, but “a lot of people in industry kind of ignored them,” says Sun. That’s because as they heat up, the index of refraction shifts and they drift away from the desired wavelength. The team developed active thermal stabilization to overcome this. The stabilization system includes a separate photodetector and a digital controller. When the detector notices a change in the amount of photocurrent coming to it, the controller alters the voltage across the micro-ring, which changes how much heat it dissipates.

Another aspect of the design requires etching away some of the silicon substrate. Because the oxide layer is so thin, the light passes through it to the substrate, which carries it away. Removing the substrate reduces that loss. However, the team leaves the silicon in place under the microprocessor and memory, where no light is coming out anyway, so they can attach a heat sink. The lack of silicon also allows them to deliver light from an external laser to power the optical components, even though the chip is bonded face down to the printed circuit board.

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Curved waveguide created which is able to significantly bend X-ray beams

Curved waveguide created which is able to significantly bend X-ray beams | Amazing Science |
A team of researchers working in Germany and France has demonstrated a way to bend X-ray beams using curved wave guides. In their paper published in Physical Review Letters, the team describes how they created the wave guides, the parameters they used in creating them and the results of their testing.

Light can be used to send signals through a fiber cable because the indices of refraction of air and glass are so different—light inside a fiber cable is reflected back into the hollow tunnel as turns are encountered. This is not the case for X-rays, however, because the index of refraction for it in solid materials is just a little bit less than for that of air. Subsequently, X-ray devices are typically extremely straight-lined. Now, the researchers with this new effort report that they have found a way to bend X-ray beams, possibly paving the way for their use in a wide variety of applications.

The key to bending X-ray beams, the team reports, is in sending them through a sufficiently narrow channel—narrow enough to limit the beam's maximum angle of deflection. Also, the device used to create the beam must be extremely precise.

To test their ideas, they created wave guides by etching 100nm wide curved channels onto 5x5mm squares of tantalum, which they then fired X-rays through. Their first runs involved radii curvatures of 10 to 80 mm with beams sent at Hamburg's DESY laboratory. In so doing, they found they were able to bend X-rays at up to 18 degrees. Emboldened, they etched more waveguides with channel radii curvatures of 1–30 mm and then tested them by firing X-rays through them at the European Synchrotron Radiation Facility in France. This time they were able to bend the beams to 30 degrees. Not all of the X-rays in the beam that are sent make it through the channel, of course, some are absorbed or tunnel their way through the metal—but, the team reports, enough makes it through for the waveguides to be useful in devices such as interferometers or other high-resolution applications.

The team plans to continue their work with the waveguides, confident that they can lessen leakage by using different materials, and possibly covering the channel. They suggest it might be possible to bend X-rays to even higher angles, from 90 to perhaps 180 degrees.

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Echoless light could help send signals through walls and skin

Echoless light could help send signals through walls and skin | Amazing Science |

A new method of making packets of light that don't echo inside optical fibers could be used to improve everything from medical imaging to laser communications.

It’s a call with no response. A new way of creating waves – whether of light, radio or sound – that don’t echo promises to improve everything from your Wi-Fi signal to medical imaging to shining lasers through space.

As a wave travels – think of light shining through water, for example – it can become scattered. This is a problem intelecommunications: if you send digital signals down a very long optical fibre, the pulses can get stretched out, and 1s can start to blend into 0s.

In 1948, physicist Leonard Eisenbud proposed a particular way of transmitting the waves to overcome this. But not until now have researchers made it happen. “The trick is that you put it in as a fancy shape, and then the sound doesn’t get distorted,” says Joel Carpenter at the University of Queensland in Brisbane, Australia. “There are no echoes: it arrives all at once at the output.”

The team started with a 100-metre-long fibre optic cable that was thin enough that light travelling through would bounce around inside, just as sound would if sent through a narrow pipe. When the light emerged at the other end, short pulses had become stretched out.

They measured exactly how the light was distorted, and crucially, how the profile of the pulse changed on its journey through the fibre. The profile at any cross section through the fibre could look like a round dot, a few dots or something more complicated, and it determines what path the photons take down the fibre, and how they interfere as they bounce around, Carpenter says.

Via Levin Chin
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The multi-colored photons that might change quantum information science

The multi-colored photons that might change quantum information science | Amazing Science |

With leading corporations now investing in highly expensive and complex infrastructures to unleash the power of quantum technologies, INRS researchers have achieved a breakthrough in a light-weight photonic system created using on-chip devices and off-the-shelf telecommunications components. In their paper published in Nature, the team demonstrates that photons can become an accessible and powerful quantum resource when generated in the form of color-entangled quDits.


The system uses a small and cost-effective photonic chip fabricated through processes similar to those used for integrated electronics. With an on-chip micro-ring resonator excited by a laser, photons are emitted in pairs that share a complex quantum state. The photons are constructed in a state featuring a number of superimposed frequency components: The photons have several colors simultaneously, and the colors of each photon in a pair are linked (entangled), regardless of their separation distance.


With each frequency -- or color -- representing a dimension, the photons are generated on-chip as a high-dimensional quantum state (quDit). Thus far, quantum information science has largely focused on the exploitation of qubits, based on two-dimensional systems where two states are superimposed (for example, 0 AND 1 at the same time, in contrast to classical bits, which are 0 OR 1 at any time). Working in the frequency domain allows the superposition of many more states (for example, a high-dimensional photon can be red AND yellow AND green AND blue, although the photons used here were infrared for telecommunications compatibility), enhancing the amount of information in a single photon.


To date, Professor Roberto Morandotti, who leads the INRS research team, confirms the realization of a quantum system with at least one hundred dimensions using this approach, and the technology developed is readily extendable to create two-quDit systems with more than 9,000 dimensions (corresponding to 12 qubits and beyond, comparable to the state of the art in significantly more expensive/complex platforms). 


The use of the frequency domain for such quantum states enables their easy transmission and manipulation in optical fibre systems. "By merging the fields of quantum optics and ultrafast optical processing, we have shown that high-dimensional manipulation of these states is indeed possible using standard telecommunications elements like modulators and frequency filters," stresses telecommunications system expert Professor José Azaña, co-supervisor of the conducted research.

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The world’s fastest camera: When light practically stands still

The world’s fastest camera: When light practically stands still | Amazing Science |
Forget high-speed cameras capturing 100 000 images per second. A research group at Lund University in Sweden has developed a camera that can film at a rate equivalent to five trillion images per second, or events as short as 0.2 trillionths of a second. This is faster than has previously been possible.


The new super-fast film camera will therefore be able to capture incredibly rapid processes in chemistry, physics, biology and biomedicine, that so far have not been caught on film.

To illustrate the technology, the researchers have successfully filmed how light – a collection of photons – travels a distance corresponding to the thickness of a paper. In reality, it only takes a picosecond, but on film the process has been slowed down by a trillion times.


Currently, high-speed cameras capture images one by one in a sequence. The new technology is based on an innovative algorithm, and instead captures several coded images in one picture. It then sorts them into a video sequence afterwards.

In short, the method involves exposing what you are filming (for example a chemical reaction) to light in the form of laser flashes where each light pulse is given a unique code. The object reflects the light flashes which merge into the single photograph. They are subsequently separated using an encryption key.


The film camera is initially intended to be used by researchers who literally want to gain better insight into many of the extremely rapid processes that occur in nature. Many take place on a picosecond and femtosecond scale, which is unbelievably fast – the number of femtoseconds in one second is significantly larger than the number of seconds in a person’s life-time.


“This does not apply to all processes in nature, but quite a few, for example, explosions, plasma flashes, turbulent combustion, brain activity in animals and chemical reactions. We are now able to film such extremely short processes”, says Elias Kristensson. “In the long term, the technology can also be used by industry and others”.

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Silicon Photonics Helps to Produce Simple Near-Perfect Mirrors

Silicon Photonics Helps to Produce Simple Near-Perfect Mirrors | Amazing Science |

Using a layer of self-assembled particles allows researcher to etch an almost-perfect reflector. Using a metamaterial created out of silicon, scientists have created a way to create an almost-perfect reflector that would be used for lasers and telescopes.


The world has become increasingly fascinated with worlds beyond our own, more so, the cosmos. To get a better understanding of the stars and planets/exoplanets near and far, scientists require the best telescopes that will reflect perfect light.


Recently published in ACS Photonics of 8 May 2015, advantages have been taken from dielectric metamaterials than plasmonic materials because it offers low-loss alternatives.

With the help of this material and the focus on an alternative method, it helps separate the electric and magnetic resonances to achieve the required reflection bandwidth while maintaining high tolerance to disorder. In other words, the material helps produce a sharper more accurate reflection while allowing scientists to scan different bandwidths with ease, with high resolution and very very minimal loss.

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Scientists count microscopic particles without microscope

Scientists count microscopic particles without microscope | Amazing Science |

Scientists from Russia and Australia have put forward a simple new way of counting microscopic particles in optical materials by means of a laser. A light beam passing through such a material splits and forms a characteristic pattern consisting of numerous bright spots on a projection screen. The researchers found that the number of these spots corresponds exactly to the number of scattering microscopic particles in the optical material. Therefore, the structure and shape of any optical material can be determined without resorting to the use of expensive electron or atomic-force microscopy. According to the researchers, the new method will help design optical devices much faster. The work was published in Scientific Reports.


The production of optical circuits requires devices that can amplify optical signals, bring them into focus, rotate and change their type of motion. Ordinary lenses cannot cope with these tasks at nanoscale, so scientists are working with artificial optical materials - photonic crystals and metamaterials, which can control the propagation of light in most extraordinary ways. However, fabricating optical materials with desired properties is a laborious process that needs constant improvement.


The scientists from ITMO University, Ioffe Institute, and Australian National University for the first time suggested analyzing the structure of photonic crystals using optical diffraction method, that is, by looking at the light pattern generated while the sample is exposed to a laser beam. The study has shown that the number of these spots is equal to the number of scattering microscopic particles in the sample structure. Previously, such small particles could only be seen and counted with powerful and expensive electron or atomic-force microscopes.


"The light senses heterogeneity," says Mikhail Rybin, first author of the paper, senior researcher at the Department of Nanophotonics and Metamaterials at ITMO University.

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Photons with half-integer angular momentum are the latest twist on light

Photons with half-integer angular momentum are the latest twist on light | Amazing Science |
Surprising effect occurs when light is confined to fewer than three dimensions


Photons can have half-integer values of angular momentum when they are confined to fewer than three dimensions. That is the conclusion of physicists in Ireland, who have revived an experiment first done in the 1830s to show that photons are not limited to having just integer values of angular momentum. The discovery could have applications in quantum computing and could also boost the capacity of optical-fibre data transmission.

The angular momentum of light comes in two varieties: spin and orbital. Spin is associated with optical polarization, which is the orientation of light's electric-field oscillations. Orbital angular momentum rotates a light beam's wavefront around its propagation axis, giving it a corkscrew shape.


Individually, the two types of angular momentum come in multiples of the reduced Planck's constant, ħ. For spin, those multiples are either +1 or –1, while the orbital variety can take any integer value. To date, physicists have assumed that a photon's total angular momentum is simply the sum of these two parts and that it therefore comes in integer multiples of ħ. But in the latest research, Paul Eastham of Trinity College Dublin and colleagues have shown that the total angular momentum can in fact take on half-integer values.


Inspiration for the work, says Eastham, came from celebrations of the 200th anniversary of the birth of Irish mathematician William Hamiltonin 2005. Hamilton and physicist Humphrey Lloyd showed, in the 1830s, that a beam of light passing through a "biaxial" crystal takes on the shape of a hollow cylinder. The void at its centre is now known to be caused by the light acquiring orbital angular momentum. The bicentennial prompted renewed interest in this effect among physicists in Ireland, says Eastham, who joined Trinity College in 2009 and then started to think about exactly how such beams behave quantum-mechanically.

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New class of lasers invented

New class of lasers invented | Amazing Science |

A new class of lasers developed by a team that included physics researchers at Kansas State University could help scientists measure distances to faraway targets, identify the presence of certain gases in the atmosphere and send images of the earth from space.


These energy-efficient lasers also are portable, produce light at difficult-to-reach wavelengths and have the potential to scale to high-powered versions.


The new lasers were invented by Brian Washburn and Kristan Corwin, both associate professors of physics at Kansas State University's College of Arts & Sciences, along with Andrew Jones, a May 2012 doctoral graduate in physics, and Rajesh Kadel, a May 2014 doctoral graduate in physics. Other contributors include three University of New Mexico physics and astronomy researchers: Wolfgang Rudolf, a Regents professor and department chair, Vasudevan Nampoothiri, a research assistant professor, and Amarin Ratanavis, a doctoral student; and John Zavada, a Virginia-based optic and photonic physicist who brought them all together.


The new lasers are fiber-based and use various molecular gases to produce light. They differ from traditional glass-tube lasers, which are large and bulky, and have mirrors to reflect the light. But the novel lasers use a hollow fiber with a honeycomb structure to hold gas and to guide light. This optical fiber is filled with a molecular gas, such as hydrogen cyanide or acetylene. Another laser excites the gas and causes a molecule of the excited gas to spontaneously emit light. Other molecules in the gas quickly follow suit, which results in laser light.


"By putting the gas in a hollow core, we can have really high intensities of light without having to put such high amounts of power into the laser," Corwin said. "If you had a glass tube of that size and put light in it, the light would escape through the sides. It's actually the structure that makes it work."


The structure also allows for portability. In contrast to traditional lasers, which are fragile and cumbersome to move, the researchers' more durable fiber laser is about the thickness of a single strand of hair and can wrap around itself for compact storage and transportation. "The smallness is nice," Washburn said. "You can wrap up the coil like a string."


The invention process began when Zavada brought Washburn and Corwin, who already had expertise putting gas into hollow fibers, together with Rudolph and Nampoothiri, who were skilled in making optically pumped gas lasers.


"We thought hard about how this would all work together, and after about a year and a half, we came up with this," Corwin said.

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Physicists discover new form of light, validate decades-old quantum mechanics prediction

Physicists discover new form of light, validate decades-old quantum mechanics prediction | Amazing Science |

It’s been over 340 years since Danish physicist Ole Rømer observed that the speed of light was finite. And, to this day, photons still manage to surprise us. Last year, scientists revealed a new fundamental property of light. This year, a team of physicists from by the Trinity College Dublin and the CRANN Institute have just discovered a new form of light that refuses to behave normally, and undermines what physicists know about angular momentum.


“Angular momentum measures how much something is rotating,” one of the study’s researchers, Kyle Ballantine, told Trinity News. “For a beam of light, although traveling in a straight line it can also be rotating around its own axis.” Up until this finding, physicists thought the angular momentum of all forms of light was a multiple of Planck’s constant. Apparently, that’s not so.


To uncover this information, the researchers began by searching for new behaviors of light by shining beams through crystals to create “screw-like structures.” They used the theory of quantum mechanics to analyze these beam structures and realized that the angular momentum of the photon would be a half-integer, not a multiple of Planck’s constant.


This discovery might not sound like much, but researchers suggest that it will influence our knowledge about the very essence of light. “Our discovery will have real impacts for the study of light waves in areas such as secure optical communications,” Professor John Donegan said.


Finding a new form of light is undoubtedly exciting. However, much of the physics community’s real joy comes from validating 30-year-old theoretical physics predictions. In the 1980s, physicists speculated ways in which quantum mechanics would open doors for strange new discoveries, such as particles with fractions of their expected quantum numbers. This research provides the first validation of those predictions. “This discovery is a breakthrough for the world of physics and science alike,” said CRANN Director, Stefano Santo.


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Disposable laser: Ultra-low-cost, easy to fabricate 'lasing capsules' made with inkjet printer

Disposable laser: Ultra-low-cost, easy to fabricate 'lasing capsules' made with inkjet printer | Amazing Science |

"Since lasers were invented more than 50 years ago, they have transformed a diverse swath of technology—from CD players to surgical instruments."

"Now researchers from France and Hungary have invented a way to print lasers that's so cheap, easy and efficient they believe the core of the laser could be disposed of after each use. The team reports its findings in the Journal of Applied Physics.

"The low-cost and easiness of laser chip fabrication are the most significant aspects of our results," said Sébastien Sanaur, an associate professor in the Center of Microelectronics in Provence at the Ecole Nationale Supérieure des Mines de Saint-Étienne in France.

Sanaur and his colleagues made organic lasers, which amplify light with carbon-containing materials. Organic lasers are not as common as inorganic lasers, like those found in laser pointers, DVD players, and optical mice, but they offer benefits such as high-yield photonic conversion, easy fabrication, low-cost and a wide range of wavelengths."

Via Mariaschnee
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How to twist light into a Möbius strip

How to twist light into a Möbius strip | Amazing Science |
Topological curiosity created from laser beam


Möbius strips can easily be made at home – just take a strip of paper, give it a half-twist and then join its ends together. Trivial as it may sound, this loop possesses the unusual property of having only one surface and one edge. They also appear very rarely in nature and had never before been seen in light. Now, an international group of physicists has created such shapes using the polarization of laser light, and the researchers say that these electromagnetic patterns could be used to build new kinds of small-scale structure such as metamaterials.


The possibility of making an optical Möbius strip was suggested in 2005 by Isaac Freund of Bar-Ilan University in Israel. Freund calculated that a pair of laser beams could be manipulated such that the axis along which their combined electric fields oscillates – the polarization vector – would trace out a Möbius strip. He proposed using beams with different spin and orbital angular momenta, and making them interfere at specific angles to one another. The spin – or circular polarization – of an electromagnetic wave involves its polarization rotating clockwise or anticlockwise in a circle that is normal to the direction of propagation. Orbital angular momentum, on the other hand, comes from the twisting of a beam's wavefront around its propagation axis.


Normally, a light wave vibrates in a plane at right angles to its direction of travel; but crucial to creating a 3D optical pattern such as a Möbius strip is to ensure that it also has a longitudinal component along the propagation axis. It turns out that Freund's proposal for creating this longitudinal component is extremely challenging from an experimental point of view, so in this latest work Peter Banzer of the Max Planck Institute for the Science of Light in Erlangen and colleagues in Germany, Canada, Italy and the US have taken a different approach.


Banzer and colleagues used a liquid-crystal device known as a q-plate. When exposed to a beam with a certain spin, a q-plate transforms that beam so that it has opposite spin and 2q units of orbital angular momentum, where q can be any half-integer value and is a property of the particular plate used. The team used a green laser beam that was a superposition of two waves with opposing spin. The result was a beam with a polarization that varied across its width. It was circularly polarized at its centre, but linearly polarized – and with varying orientations of the polarization vector – further out.


To extend this 2D pattern of polarizations into the third dimension, the researchers sent the beam through a tight-focusing microscope lens. This gave the beam a longitudinal component – the size of which depended on the degree of focusing. The result was a Möbius strip of polarization that measured just 200–250 nm across. By changing the q-plate, the researchers were able to create Möbius strips with three (q = –1/2) and five half turns (q = –3/2). "It was a puzzle in the community as to whether such a topology could exist physically or whether it was just a mathematical description," says group member Ebrahim Karimi of the University of Ottawa. "But now we have seen this in the lab, we know that Freund's theory is correct."

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Characterizing quantum Hall light zooming around a photonic chip

Characterizing quantum Hall light zooming around a photonic chip | Amazing Science |

The quantum Hall effect is best understood by peering through the lens of topology. In the 1980s, physicists discovered that electrons in some materials behave strangely when subjected to large magnetic fields at extreme cryogenic temperatures. Remarkably, the electrons at the boundary of the material will flow along avenues of travel called ‘edge states’, protected against defects that are most certainly present in the material. Moreover, the conductance--a measure of the current--is quantized. This means that when the magnetic field is ramped up, then the conductance does not change smoothly. Instead it stays flat, like a plateau, and then suddenly jumps to a new value. The plateaus occur at precise values that are independent of many of the material’s properties. This hopping behavior is a form of precise quantization and is what gives the quantum Hall effect its great utility, allowing it to provide the modern standard for calibrating resistance in electronics, for instance.


Researchers have engineered quantum Hall behavior in other platforms besides the solid-state realm in which it was originally discovered. Signatures of such physics have been spotted in ultracold atomic gases and photonics, where light travels in fabricated chips. Hafezi and colleagues have led the charge in the photonics field.


The group uses a silicon-based chip that is filled with an array of ring-shaped structures called resonators. The resonators are connected to each other via waveguides (figure). The chip design strictly determines the conditions under which light can travel along the edges rather than through the inner regions. The researchers measure the transmission spectrum, which is the fraction of light that successfully passes through an edge pathway. To circulate unimpeded through the protected edge modes, the light must possess a certain energy. The transmission increases when the light energy matches this criteria. For other parameters, the light will permeate the chip interior or get lost, causing the transmission signal to decrease. The compiled transmission spectrum looks like a set of bright stripes separated by darker regions (see figure). Using such a chip, this group previously collected images of light traveling in edge states, definitively demonstrating the quantum Hall physics for photons.


In this new experiment Hafezi’s team modified their design to directly measure the value of the topology-related property that characterizes the photonic edge states. This measurement is analogous to characterizing the quantized conductance, which was critical to understanding the electron quantum Hall effect. In photonics, however, conductance is not relevant as it pertains to electron-like behavior. Here the significant feature is the winding number, which is related to how light circulates around the chip. Its value equals to the number of available edge states and should not change in the face of certain disruptions.


To extract the winding number, the team adds 100 nanometer titanium heaters on a layer above the waveguides. Heat changes the index of refraction, namely how the light bends as it passes through the waveguides. In this manner, researchers can controllably imprint a phase shift onto the light. Phase can be thought of in terms of a time delay. For instance, when comparing two light waves, the intensity can be the same, but one wave may be shifted in time compared to the other. The two waves overlap when one wave is delayed by a full oscillation cycle—this is called a 2π phase shift.


On the chip, enough heat is added to add a 2π phase shift to the light. The researchers observe an energy shift in the transmission stripes corresponding to light traveling along the edge. Notably, in this chip design, the light can circulate either clockwise (CW) or counterclockwise (CCW), and the two travel pathways do not behave the same (in contrast to an interferometer). When the phase shift is introduced, the CW traveling light hops one direction in the transmission spectrum, and the CCW goes the opposite way. The winding number is the amount that these edge-state spectral features move and is exactly equivalent to the quantized jumps in the electronic conductance.


Sunil Mittal, lead author and postdoctoral researcher explains one future direction, “So far, our research has been focused on transporting classical [non-quantum] properties of light--mainly the power transmission. It is intriguing to further investigate if this topological system can also achieve robust transport of quantum information, which will have potential applications for on-chip quantum information processing.” 

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Building 'invisible' materials with light

Building 'invisible' materials with light | Amazing Science |

A new method of building materials using light, developed by researchers at the University of Cambridge, could one day enable technologies that are often considered the realm of science fiction, such as invisibility cloaks and cloaking devices.

Although cloaked starships won't be a reality for quite some time, the technique which researchers have developed for constructing materials with building blocks a few billionths of a meter across can be used to control the way that light flies through them, and works on large chunks all at once. Details are published today (28 July, 2015) in the journal Nature Communications.

The key to any sort of 'invisibility' effect lies in the way light interacts with a material. When light hits a surface, it is either absorbed or reflected, which is what enables us to see objects. However, by engineering materials at the nanoscale, it is possible to produce 'metamaterials': materials which can control the way in which light interacts with them. Light reflected by a metamaterial is refracted in the 'wrong' way, potentially rendering objects invisible, or making them appear as something else.

Metamaterials have a wide range of potential applications, including sensing and improving military stealth technology. However, before cloaking devices can become reality on a larger scale, researchers must determine how to make the right materials at the nanoscale, and using light is now shown to be an enormous help in such nano-construction.

The technique developed by the Cambridge team involves using unfocused laser light as billions of needles, stitching gold nanoparticles together into long strings, directly in water for the first time. These strings can then be stacked into layers one on top of the other, similar to Lego bricks. The method makes it possible to produce materials in much higher quantities than can be made through current techniques.

In order to make the strings, the researchers first used barrel-shaped molecules called cucurbiturils (CBs). The CBs act like miniature spacers, enabling a very high degree of control over the spacing between the nanoparticles, locking them in place.

In order to connect them electrically, the researchers needed to build a bridge between the nanoparticles. Conventional welding techniques would not be effective, as they cause the particles to melt. "It's about finding a way to control that bridge between the nanoparticles," said Dr Ventsislav Valev of the University's Cavendish Laboratory, one of the authors of the paper. "Joining a few nanoparticles together is fine, but scaling that up is challenging."

The key to controlling the bridges lies in the cucurbiturils: the precise spacing between the nanoparticles allows much more control over the process. When the laser is focused on the strings of particles in their CB scaffolds, it produces plasmons: ripples of electrons at the surfaces of conducting metals. These skipping electrons concentrate the light energy on atoms at the surface and join them to form bridges between the nanoparticles. Using ultrafast lasers results in billions of these bridges forming in rapid succession, threading the nanoparticles into long strings, which can be monitored in real time.

"We have controlled the dimensions in a way that hasn't been possible before," said Dr Valev, who worked with researchers from the Department of Chemistry and the Department of Materials Science & Metallurgy on the project. "This level of control opens up a wide range of potential practical applications."

Via Anne Pascucci, MPA, CRA, Mark E. Deschaine, PhD, Jocelyn Stoller
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The world's fastest nanoscale photonics switch

The world's fastest nanoscale photonics switch | Amazing Science |
An international team of researchers from Lomonosov Moscow State University and the Australian National University in Canberra created an ultrafast all-optical switch on silicon nanostructures. This device may become a platform for future computers and permit to transfer data at an ultra-high speed. An article with the description of the device was published in the Nano Letters journal and highlighted in Nature Materials.

Three years ago, several groups of researchers simultaneously discovered an important effect: They found out that silicon nanoparticles exhibit strong resonances in the visible spectrum—the so-called magnetic dipole resonances. This type of resonance is characterized by strong localization of light waves on subwavelength scales, inside the nanoparticles. This effect turned out to be interesting to research, but, according to Maxim Shcherbakov, the first author of the article published in Nano Letters, nobody thought that this discovery could lead to the development of a compact and very rapid photonic switch.

Nanoparticles were fabricated in the Australian National University by e-beam lithography followed by plasma-phase etching. It was done by Alexander Shorokhov, who served an internship in the University as a part of Presidential scholarship for studying abroad. The samples were brought to Moscow, and all the experimental work was carried out at the Faculty of Physics of Lomonosov Moscow State University, in the Laboratory of Nanophotonics and Metamaterials.

"In our experimental research, me and my colleague, Polina Vabishchevich from the faculty, used a set of nonlinear optics methods that address femtosecond light matter," explains Maxim Shcherbakov. "We used our femtosecond laser complex, acquired as part of the MSU development program".

Eventually, researchers developed a device: a disc 250 nm in diameter that is capable of switching optical pulses at femtosecond rates (femtosecond is a one millionth of one billionth of a second). Switching speeds that fast enable data transmission and processing devices that will work at tens and hundreds terabits per second. This can make possible downloading thousands of HD movies in less than a second.

The operation of the all-optical switch created by MSU researchers is based on the interaction between two femtosecond pulses. The interaction results from the magnetic resonance of the silicon nanostructures. If the pulses arrive at the nanostructure simultaneously, one of them interacts with the other and dampens it due to the effect of two-photon absorption. If there is a 100-fs delay between the two pulses, the interaction does not occur, and the second pulse goes through the nanostructure without changing.

"We were able to develop a structure with the undesirable free-carrier effects are suppressed," says Maxim Shcherbakov. "Free carriers (electrons and electron holes) place serious restrictions on the speed of signal conversion in the traditional integrated photonics. Our work represents an important step towards novel and efficient active photonic devices— transistors, logic units, and others. Features of the technology implemented in our work will allow its use in silicon photonics. In the near future, we are going to test such nanoparticles in integrated circuits".

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