Tag Archives: light

A new nanoparticle—layered* like an onion

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The new nanoparticle comes courtesy of an international collaboration (US, China, Sweden, and Russia. A Nov. 10, 2015 University of Buffalo news release (also on EurekAlert) by Charlotte Hu describes the particle and its properties,

A new, onion-like nanoparticle could open new frontiers in biomaging, solar energy harvesting and light-based security techniques.

The particle’s innovation lies in its layers: a coating of organic dye, a neodymium-containing shell, and a core that incorporates ytterbium and thulium. Together, these strata convert invisible near-infrared light to higher energy blue and UV light with record-high efficiency, a trick that could improve the performance of technologies ranging from deep-tissue imaging and light-induced therapy to security inks used for printing money.

Here’s an artist’s representation of the new nanoparticle,

An artist’s rendering shows the layers of a new, onion-like nanoparticle whose specially crafted layers enable it to efficiently convert invisible near-infrared light to higher energy blue and UV light. Credit: Kaiheng Wei Courtesy: University of Buffalo

An artist’s rendering shows the layers of a new, onion-like nanoparticle whose specially crafted layers enable it to efficiently convert invisible near-infrared light to higher energy blue and UV light. Credit: Kaiheng Wei Courtesy: University of Buffalo

The news release goes on to describe technology in more detail,

When it comes to bioimaging, near-infrared light could be used to activate the light-emitting nanoparticles deep inside the body, providing high-contrast images of areas of interest. In the realm of security, nanoparticle-infused inks could be incorporated into currency designs; such ink would be invisible to the naked eye, but glow blue when hit by a low-energy laser pulse — a trait very difficult for counterfeiters to reproduce.

“It opens up multiple possibilities for the future,” says Tymish Ohulchanskyy, deputy director of photomedicine and research associate professor at the Institute for Lasers, Photonics, and Biophotonics (ILPB) at the University at Buffalo.

“By creating special layers that help transfer energy efficiently from the surface of the particle to the core, which emits blue and UV light, our design helps overcome some of the long-standing obstacles that previous technologies faced,” says Guanying Chen, professor of chemistry at Harbin Institute of Technology [China] and ILPB research associate professor.

“Our particle is about 100 times more efficient at ‘upconverting’ light than similar nanoparticles created in the past, making it much more practical,” says Jossana Damasco, a UB chemistry PhD student who played a key role in the project.

The research was published online in Nano Letters on Oct. 21 and led by the Institute for Lasers, Photonics, and Biophotonics at UB, and the Harbin Institute of Technology in China, with contributions from the Royal Institute of Technology in Sweden; Tomsk State University in Russia; and the University of Massachusetts Medical School.

The study’s senior author was Paras Prasad, ILPB executive director and SUNY [State University of New York] Distinguished Professor in chemistry, physics, medicine and electrical engineering at UB.

Peeling back the layers

Converting low-energy light to light of higher energies isn’t easy to do. The process involves capturing two or more tiny packets of light called “photons” from a low-energy light source, and combining their energy to form a single, higher-energy photon.

The onionesque nanoparticle performs this task beautifully. Each of its three layers fulfills a unique function:

  • The outermost layer is a coating of organic dye. This dye is adept at absorbing photons from low-energy near-infrared light sources. It acts as an “antenna” for the nanoparticle, harvesting light and transferring energy inside, Ohulchanskyy says.
  • The next layer is a neodymium-containing shell. This layer acts as a bridge, transferring energy from the dye to the particle’s light-emitting core.
  • Inside the light-emitting core, ytterbium and thulium ions work in concert. The ytterbium ions draw energy into the core and pass the energy on to the thulium ions, which have special properties that enable them to absorb the energy of three, four or five photons at once, and then emit a single higher-energy photon of blue and UV light.

So why not just use the core? Why add the dye and neodymium layer at all?

As Ohulchanskyy and Chen explain, the core itself is inefficient in absorbing photons from the outside world. That’s where the dye comes in.

Once you add the dye, the neodymium-containing layer is necessary for transferring energy efficiently from dye to core. Ohulchanskyy uses the analogy of a staircase to explain why this is: When molecules or ions in a material absorb a photon, they enter an “excited” state from which they can transfer energy to other molecules or ions. The most efficient transfer occurs between molecules or ions whose excited states require a similar amount of energy to obtain, but the dye and ytterbium ions have excited states with very different energies. So the team added neodymium — whose excited state is in between that of the dye and thulium’s — to act as a bridge between the two, creating a “staircase” for the energy to travel down to reach emitting thulium ions.

Here’s a link to and a citation for the paper,

Energy-Cascaded Upconversion in an Organic Dye-Sensitized Core/Shell Fluoride Nanocrystal by Guanying Chen, Jossana Damasco, Hailong Qiu, Wei Shao, Tymish Y. Ohulchanskyy, Rashid R. Valiev, Xiang Wu, Gang Han, Yan Wang, Chunhui Yang, Hans Ågren, and Paras N. Prasad. Nano Lett., 2015, 15 (11), pp 7400–7407 DOI: 10.1021/acs.nanolett.5b02830 Publication Date (Web): October 21, 2015

Copyright © 2015 American Chemical Society

This paper is behind a paywall.

Finally, there is a Nov. 11, 2015 article about the research by Jake Wilkinson for Azonano. He provides additional details such as this measurement,

Measuring approximately 50nm in diameter, the new nanoparticle features three differently designed layers. …

*’ayered’ changed to ‘layered’ on Nov. 11, 2015.

Interfaces are the device—organic semiconductors and their edges

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Researchers at the University of British Columbia (UBC; Canada) have announced a startling revelation according to an Oct. 6, 2015 news item on ScienceDaily,

As the push for thinner and faster electronics continues, a new finding by University of British Columbia scientists could help inform the design of the next generation of cheaper, more efficient devices.

The work, published this week in Nature Communications, details how electronic properties at the edges of organic molecular systems differ from the rest of the material.

An Oct. 6, 2015 UBC news release on EurekAlert, which originated the news item, expands on the theme,

Organic [as in carbon-based] materials–plastics–are of great interest for use in solar panels, light emitting diodes and transistors. They’re low-cost, light, and take less energy to produce than silicon. Interfaces–where one type of material meets another–play a key role in the functionality of all these devices.

“We found that the polarization-induced energy level shifts from the edge of these materials to the interior are significant, and can’t be neglected when designing components,” says UBC PhD researcher Katherine Cochrane, lead author of the paper.

‘While we were expecting some differences, we were surprised by the size of the effect and that it occurred on the scale of a single molecule,” adds UBC researcher Sarah Burke, an expert on nanoscale electronic and optoelectronic materials and author on the paper.

The researchers looked at ‘nano-islands’ of clustered organic molecules. The molecules were deposited on a silver crystal coated with an ultra-thin layer of salt only two atoms deep. The salt is an insulator and prevents electrons in the organic molecules from interacting with those in the silver–the researchers wanted to isolate the interactions of the molecules.

Not only did the molecules at the edge of the nano-islands have very different properties than in the middle, the variation in properties depended on the position and orientation of other molecules nearby.

The researchers, part of UBC’s Quantum Matter Institute, used a simple, analytical model to explain the differences which can be extended to predict interface properties in much more complex systems, like those encountered in a real device.

“Herbert Kroemer said in his Nobel Lecture that ‘The interface is the device’ and it’s equally true for organic materials,” says Burke. [emphasis mine] “The differences we’ve seen at the edges of molecular clusters highlights one effect that we’ll need to consider as we design new materials for these devices, but likely they are many more surprises waiting to be discovered.”

Cochrane and colleagues plan to keep looking at what happens at interfaces in these materials and to work with materials chemists to guide the design rules for the structure and electronic properties of future devices.

Methods

The experiment was performed at UBC’s state-of-the-art Laboratory for Atomic Imaging Research, which features three specially designed ultra-quiet rooms that allow the instruments to sit in complete silence, totally still, to perform their delicate measurements. This allowed the researchers to take dense data sets with a tool called a scanning tunnelling microscope (STM) that showed them the energy levels in real-space on the scale of single atoms.

Here’s a link to and a citation for the paper,

Pronounced polarization-induced energy level shifts at boundaries of organic semiconductor nanostructures by K. A. Cochrane, A. Schiffrin, T. S. Roussy, M. Capsoni, & S. A. Burke. Nature Communications 6, Article number: 8312 doi:10.1038/ncomms9312 Published 06 October 2015

This paper is open access. Yes, I borrowed from Nobel Laureate, Herbert Kroemer for the headline. As Woody Guthrie (legendary American folksinger) once said, more or less, “Only steal from the best.”

Nanoscale device emits light as powerfully as an object 10,000 times its size

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The potential application in the field of solar power is what most interests me in this collaborative research from the University of Wisconsin-Madison (US) and Fudan University in China. From a July 13, 2015 news item on ScienceDaily,

University of Wisconsin-Madison engineers have created a nanoscale device that can emit light as powerfully as an object 10,000 times its size. It’s an advance that could have huge implications for everything from photography to solar power.

In a paper published July 10 [2015] in the journal Physical Review Letters, Zongfu Yu, an assistant professor of electrical and computer engineering, and his collaborators describe a nanoscale device that drastically surpasses previous technology in its ability to scatter light. They showed how a single nanoresonator can manipulate light to cast a very large “reflection.” The nanoresonator’s capacity to absorb and emit light energy is such that it can make itself — and, in applications, other very small things — appear 10,000 times as large as its physical size.

A July 13, 2015 University of Wisconsin-Madison news release (also on EurekAlert) by Scott Gordon, which originated the news item, expands on the theme,

“Making an object look 10,000 times larger than its physical size has lots of implications in technologies related to light,” Yu says.

The researchers realized the advance through materials innovation and a keen understanding of the physics of light. Much like sound, light can resonate, amplifying itself as the surrounding environment manipulates the physical properties of its wave energy. The researchers took advantage of this by creating an artificial material in which the wavelength of light is much larger than in a vacuum, which allows light waves to resonate more powerfully.

The device condenses light to a size smaller than its wavelength, meaning it can gather a lot of light energy, and then scatters the light over a very large area, harnessing its output for imaging applications that make microscopic particles appear huge.

“The device makes an object super-visible by enlarging its optical appearance with this super-strong scattering effect,” says Ming Zhou, a Ph.D. student in Yu’s group and lead author of the paper.

Much as a very thin string on a guitar can absorb a large amount of acoustic energy from its surroundings and begin to vibrate in sympathy, this one very small optical device can receive light energy from all around and yield a surprisingly strong output. In imaging, this presents clear advantages over conventional lenses, whose light-gathering capacity is limited by direction and size.

“We are developing photodetectors based on this technology and, for example, it could be helpful for photographers wanting to shoot better quality pictures in weak light conditions,” Yu says.

Given the nanoresonator’s capacity to absorb large amounts of light energy, the technology also has potential in applications that harvest the sun’s energy with high efficiency. In addition, Yu envisions simply letting the resonator emit that energy in the form of infrared light toward the sky, which is very cold. Because the nanoresonator has a large optical cross-section — that is, an ability to emit light that dramatically exceeds its physical size — it can shed a lot of heat energy, making for a passive cooling system.

“This research opens up a new way to manipulate the flow of light, and could enable new technologies in light sensing and solar energy conversion,” Yu says.

Here’s a link to and a citation for the paper,

Extraordinarily Large Optical Cross Section for Localized Single Nanoresonator by Ming Zhou, Lei Shi, Jian Zi, and Zongfu Yu. Phys. Rev. Lett. 115, 023903  DOI: http://dx.doi.org/10.1103/PhysRevLett.115.023903 Published 10 July 2015

This paper is behind a paywall.

Converting light to electricity at femto speeds

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This is a pretty remarkable (to me anyway) piece of research on speeding up the process of converting light to electricity. From an April 14, 2015 Institute of Photonic Science press release (also on EurekAlert but dated April 15, 2015),

The efficient conversion of light into electricity plays a crucial role in many technologies, ranging from cameras to solar cells. It also forms an essential step in data communication applications, since it allows for information carried by light to be converted into electrical information that can be processed in electrical circuits. Graphene is an excellent material for ultrafast conversion of light to electrical signals, but so far it was not known how fast graphene responds to ultrashort flashes of light.

…

The new device that the researchers developed is capable of converting light into electricity in less than 50 femtoseconds (a twentieth of a millionth of a millionth of a second). To do this, the researchers used a combination of ultrafast pulse-shaped laser excitation and highly sensitive electrical readout. As Klaas-Jan Tielrooij comments, “the experiment uniquely combined the ultrafast pulse shaping expertise obtained from single molecule ultrafast photonics with the expertise in graphene electronics. Facilitated by graphene’s nonlinear photo-thermoelectric response, these elements enabled the observation of femtosecond photodetection response times.”

The ultrafast creation of a photovoltage in graphene is possible due to the extremely fast and efficient interaction between all conduction band carriers in graphene. This interaction leads to a rapid creation of an electron distribution with an elevated electron temperature. Thus, the energy absorbed from light is efficiently and rapidly converted into electron heat. Next, the electron heat is converted into a voltage at the interface of two graphene regions with different doping. This photo-thermoelectric effect turns out to occur almost instantaneously, thus enabling the ultrafast conversion of absorbed light into electrical signals. As Prof. van Hulst states, “it is amazing how graphene allows direct non-linear detecting of ultrafast femtosecond (fs) pulses”.

The results obtained from the findings of this work, which has been partially funded by the EC Graphene Flagship, open a new pathway towards ultra-fast optoelectronic conversion. As Prof. Koppens comments, “Graphene photodetectors keep showing fascinating performances addressing a wide range of applications”.

Here’s a link to and a citation for the paper,

Generation of photovoltage in graphene on a femtosecond timescale through efficient carrier heating by K. J. Tielrooij, L. Piatkowski, M. Massicotte, A. Woessner, Q. Ma, Y. Lee,  K. S. Myhro, C. N. Lau, P. Jarillo-Herrero, N. F. van Hulst & F. H. L. Koppens. Nature Nanotechnology (2015) doi:10.1038/nnano.2015.54 Published online 13 April 2015

This paper is behind a paywall but there is a free preview via ReadCube Access.

Masterpieces seen in a new light

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Caption: This image shows: After Raphael 1483 - 1520 probably before 1600 Oil on wood 87 x 61.3 cm Wynn Ellis Bequest, 1876 Credit: © National Gallery, London

Caption: This image shows: After Raphael 1483 – 1520
probably before 1600
Oil on wood
87 x 61.3 cm
Wynn Ellis Bequest, 1876
Credit: © National Gallery, London

An April 13, 2015 Optical Society news release (also on EurekAlert) describes a new technique for ‘seeing’ below the surface of a painting without taking samples,

A painting hanging on the wall in an art gallery tells one story. What lies beneath its surface may tell quite another.

Often in a Rembrandt, a Vermeer, a Leonardo, a Van Eyck, or any other great masterpiece of western art, the layers of paint are covered with varnish, sometimes several coats applied at different times over their history. The varnish was originally applied to protect the paint underneath and make the colors appear more vivid, but over the centuries it can degrade. Conservators carefully clean off the old varnish and replace it with new, but to do this safely it is useful to understand the materials and structure of the painting beneath the surface. Conservation scientists can glean this information by analyzing the hidden layers of paint and varnish.

Now, researchers from Nottingham Trent University’s School of Science and Technology have partnered with the National Gallery in London to develop an instrument capable of non-invasively capturing subsurface details from artwork at a high resolution. Their setup, published in an Optics Express paper, will allow conservators and conservation scientists to more effectively peek beneath the surface of paintings and artifacts to learn not only how the artist built up the original composition, but also what coatings have been applied to it over the years.

Traditionally, analyzing the layers of a painting requires taking a very small physical sample — usually around a quarter of a millimeter across — to view under a microscope. The technique provides a cross-section of the painting’s layers, which can be imaged at high resolution and analyzed to gain detailed information on the chemical composition of the paint, but does involve removing some original paint, even if only a very tiny amount. When studying valuable masterpieces, conservation scientists must therefore sample very selectively from already-damaged areas, often only taking a few minute samples from a large canvas.

More recently, researchers have begun to use non-invasive imaging techniques to study paintings and other historical artifacts. For example, Optical Coherence Tomography (OCT) was originally developed for medical imaging but has also been applied to art conservation. Because it uses a beam of light to scan the intact painting without removing physical samples, OCT allows researchers to analyze the painting more extensively. However, the spatial resolution of commercially-available OCT setups is not high enough to fully map the fine layers of paint and varnish.

The Nottingham Trent University researchers gave OCT an upgrade. “We’re trying to see how far we can go with non-invasive techniques. We wanted to reach the kind of resolution that conventional destructive techniques have reached,” explained Haida Liang, who led the project.

In OCT, a beam of light is split: half is directed towards the sample, and the other half is sent to a reference mirror. The light scatters off both of these surfaces. By measuring the combined signal, which effectively compares the returned light from the sample versus the reference, the apparatus can determine how far into the sample the light penetrated. By repeating this procedure many times across an area, researchers can build up a cross-sectional map of the painting.

Liang and her colleagues used a broadband laser-like light source — a concentrated beam of light containing a wide range of frequencies. The wider frequency range allows for more precise data collection, but such light sources were not commercially available until recently.

Along with a few other modifications, the addition of the broadband light source enabled the apparatus to scan the painting at a higher resolution. When tested on a late 16th-century copy of a Raphael painting, housed at the National Gallery in London, it performed as well as traditional invasive imaging techniques.

“We are able to not only match the resolution but also to see some of the layer structures with better contrast. That’s because OCT is particularly sensitive to changes in refractive index,” said Liang. In some places, the ultra-high resolution OCT setup identified varnish layers that were almost indistinguishable from each other under the microscope.

Eventually, the researchers plan to make their instrument available to other art institutions. It could also be useful for analyzing historical manuscripts, which cannot be physically sampled in the same way that paintings can.

In a parallel paper recently published in Optics Express, the researchers also improved the depth into the painting that their apparatus can scan. The two goals are somewhat at odds: using a longer wavelength light source could enhance the penetration depth, but shorter wavelength light (as used in their current setup) provides the best resolution.

“The next challenge is perhaps to be able to do that in one instrument, as well as to extract chemical information from different layers,” said Liang.

Here are links to and citations for the two recent papers published by Liang and her team,

Ultra-high resolution Fourier domain optical coherence tomography for old master paintings by C. S. Cheung, M. Spring, and H. Liang. Optics Express, Vol. 23, Issue 8, pp. 10145-10157 (2015) http://dx.doi.org/10.1364/OE.23.010145

High resolution Fourier domain optical coherence tomography in the 2 μm wavelength range using a broadband supercontinuum source by C. S. Cheung, J. M. O. Daniel, M. Tokurakawa, W. A. Clarkson, and H. Liang. Optics Express, Vol. 23, Issue 3, pp. 1992-2001 (2015) http://dx.doi.org/10.1364/OE.23.001992

Both papers are open access.

Building architecture inspires new light-bending material

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Usually, it’s nature which inspires scientists but not this time. Instead, a building in Canberra, Australia has provided the inspiration according to a March 24, 2015 news item on Nanowerk,

Physicists inspired by the radical shape of a Canberra building have created a new type of material which enables scientists to put a perfect bend in light.

The creation of a so-called topological insulator could transform the telecommunications industry’s drive to build an improved computer chip using light.

Leader of the team, Professor Yuri Kivshar from The Australian National University (ANU) said the revolutionary material might also be useful in microscopes, antenna design, and even quantum computers.

“There has been a hunt for similar materials in photonics based on large complicated structures,” said Professor Kivshar, who is the head of the Nonlinear Physics Centre in ANU Research School of Physics and Engineering.

“Instead we used a simple, small-scale zigzag structure to create a prototype of these novel materials with amazing properties.”

The structure was inspired by the Nishi building near ANU, which consists of rows of offset zigzag walls.

Here’s what the building looks like,

Caption: Alex Slobozhanyuk (L) and Andrey Miroshnichenko with models of their material structures in front of the Nishi building that inspired them. Credit: Stuart Hay, ANU

Caption: Alex Slobozhanyuk (L) and Andrey Miroshnichenko with models of their material structures in front of the Nishi building that inspired them.
Credit: Stuart Hay, ANU

A March 24, 2015 Australian National University press release, which originated the news item, goes on to describe topological insulators and what makes this ‘zigzag’ approach so exciting,

Topological insulators have been initially developed for electronics, and the possibility of building an optical counterpart is attracting a lot of attention.

The original zigzag structure of the material was suggested in the team’s earlier collaboration with Dr Alexander Poddubny, from Ioffe Institute in Russia, said PhD student Alexey Slobozhanyuk.

“The zigzag structure creates a coupling throughout the material that prevents light from travelling through its centre,” Mr Slobozhanyuk said.

“Instead light is channelled to the edges of the material, where it becomes completely localised by means of a kind of quantum entanglement known as topological order.”

Fellow researcher Dr Andrew Miroshnichenko said the building inspired the researchers to think of multiple zigzags.

“We had been searching for a new topology and one day I looked at the building and a bell went off in my brain,” said fellow researcher Dr Andrey Miroshnichenko.

“On the edges of such a material the light should travel completely unhindered, surfing around irregularities that would normally scatter the light.

“These materials will allow light to be bent around corners with no loss of signal,” he said.

The team showed that the exceptional attributes of the material are related to its structure, or topology, and not to the molecules it is made from.

“In our experiment we used an array of ceramic spheres, although the initial theoretical model used metallic subwavelength particles,” said Dr Miroshnichenko.

“Even though they are very different materials they gave the same result.”

In contrast with other international groups attempting to create topological insulators with large scale structures, the team used spheres that were smaller than the wavelength of the microwaves in their successful experiments.

Dr Poddubny devised the theory when he realised there was a direct analogy between quantum Kitaev’s model of Majorana fermions and optically coupled subwavelength scatterers.

Mr Slobozhanyuk said the team could control which parts of the material surface the light is channelled to by changing the polarisation of the light.

“This opens possibilities ranging from nanoscale light sources for enhancing microscopes, highly efficient antennas or even quantum computing,” he said.

“The structure couples the two sides of the material, so they could be used as entangled qubits for quantum computing.”

It would be nice to offer a link to a published paper but I cannot find one.

Capturing the particle and the wave: photographing light

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On returning to school to get a bachelor’s degree, I registered in a communications course and my first paper was about science, light, and communication. The particle/wave situation still fascinates me (and I imagine many others).

A March 2, 2015 news item on phys.org describes the first successful photography of light as both particle and wave,

Light behaves both as a particle and as a wave. Since the days of Einstein, scientists have been trying to directly observe both of these aspects of light at the same time. Now, scientists at EPFL [École polytechnique fédérale de Lausanne in Switzerland] have succeeded in capturing the first-ever snapshot of this dual behavior.

Quantum mechanics tells us that light can behave simultaneously as a particle or a wave. However, there has never been an experiment able to capture both natures of light at the same time; the closest we have come is seeing either wave or particle, but always at different times. Taking a radically different experimental approach, EPFL scientists have now been able to take the first ever snapshot of light behaving both as a wave and as a particle. The breakthrough work is published in Nature Communications.

A March 2, 2015 EPFL press release (also on EurekAlert), which originated the news item, describes the science and the research,

When UV light hits a metal surface, it causes an emission of electrons. Albert Einstein explained this “photoelectric” effect by proposing that light – thought to only be a wave – is also a stream of particles. Even though a variety of experiments have successfully observed both the particle- and wave-like behaviors of light, they have never been able to observe both at the same time.

A research team led by Fabrizio Carbone at EPFL has now carried out an experiment with a clever twist: using electrons to image light. The researchers have captured, for the first time ever, a single snapshot of light behaving simultaneously as both a wave and a stream of particles particle.

The experiment is set up like this: A pulse of laser light is fired at a tiny metallic nanowire. The laser adds energy to the charged particles in the nanowire, causing them to vibrate. Light travels along this tiny wire in two possible directions, like cars on a highway. When waves traveling in opposite directions meet each other they form a new wave that looks like it is standing in place. Here, this standing wave becomes the source of light for the experiment, radiating around the nanowire.

This is where the experiment’s trick comes in: The scientists shot a stream of electrons close to the nanowire, using them to image the standing wave of light. As the electrons interacted with the confined light on the nanowire, they either sped up or slowed down. Using the ultrafast microscope to image the position where this change in speed occurred, Carbone’s team could now visualize the standing wave, which acts as a fingerprint of the wave-nature of light.

While this phenomenon shows the wave-like nature of light, it simultaneously demonstrated its particle aspect as well. As the electrons pass close to the standing wave of light, they “hit” the light’s particles, the photons. As mentioned above, this affects their speed, making them move faster or slower. This change in speed appears as an exchange of energy “packets” (quanta) between electrons and photons. The very occurrence of these energy packets shows that the light on the nanowire behaves as a particle.

“This experiment demonstrates that, for the first time ever, we can film quantum mechanics – and its paradoxical nature – directly,” says Fabrizio Carbone. In addition, the importance of this pioneering work can extend beyond fundamental science and to future technologies. As Carbone explains: “Being able to image and control quantum phenomena at the nanometer scale like this opens up a new route towards quantum computing.”

This work represents a collaboration between the Laboratory for Ultrafast Microscopy and Electron Scattering of EPFL, the Department of Physics of Trinity College (US) and the Physical and Life Sciences Directorate of the Lawrence Livermore National Laboratory. The imaging was carried out EPFL’s ultrafast energy-filtered transmission electron microscope – one of the two in the world.

For anyone who prefers videos, the EPFL researchers have  prepared a brief description (loaded with some amusing images) of their work,


Here’s a link to and a citation for the research paper,

Simultaneous observation of the quantization and the interference pattern of a plasmonic near-field by L Piazza, T.T.A. Lummen, E Quiñonez, Y Murooka, B.W. Reed, B Barwick & F Carbone. Nature Communications 6, Article number: 6407 doi:10.1038/ncomms7407 Published 02 March 2015

This is an open access paper.

Opals, Diana Ross, and nanophotonic hybridization

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It was a bit of a stretch to include Diana Ross in a Jan. 12, 2015 news item on Nanowerk about nanophotonic research at the University of Twente’s MESA+ Institute for Nano­technology  but I’m glad they did,

Ever since the early 1900s work of Niels Bohr and Hendrik Lorentz, it is known that atoms display characteristic resonant behavior to light. The hallmark of a resonance is its characteristic peak-trough behavior of the refractive index with optical frequency. Scientists from the Dutch MESA+ Institute for Nano­technology at the University of Twente have recently infiltrated cesium atoms in a self-assembled opal to create a hybrid nanophotonic system. By tuning the opal’s forbidden gap relative to the atomic resonance, dra­matic changes are observed in reflectivity. In the most extreme case, the atomic reflection spectrum is turned upside down[1] compared to the traditional case. Since dispersion is crucial in the control of optical signal pulses, the new results offer opportunities for optical information manipulation. As atoms are exquisite storage de­vices for light quanta, the results open vistas on quantum information processing, as well as on new nanoplasmonics.

A Jan. 12, 2015 MESA+ Institute for Nano­technology at the University of Twente press release, which originated the news item, provides an illustrative diagram and a wealth of technical detail about the research,

Courtesy of the University of Twente

Courtesy of the University of Twente

While the speed of light c is proverbial, it can readily be modified by sending light through a medium with a certain refractive index n. In the medium, the speed will be decreased by the index to c/n. In any material, the refractive index depends on the frequency of the light. Usually the refractive index increases with frequency, called normal dispersion as it prevails at most frequencies in most materials such as a glass of water, a telecom fiber, or an atomic vapor. Close to the resonance frequency of the material, the index strongly decreases, called anomalous dispersion.

Dispersion is essential to control how optical bits of information – encoded as short pulses – is manipulated optical circuits. In modern optics at the nanoscale, called nanophotonics, dispersion is controlled with classes of complex nanostruc­tures that cause novel behavior to emerge. An example is a photonic crystal fiber, which does not consist of only glass like a traditional fiber, but of an intricate arrange­ment of holes and glass nanostructures.

The Twente team led by Harding devised a hybrid system consisting of an atomic vapor infiltrated in an opal photonic crystal. Photonic crystals have attracted considerable attention for their ability to radically control propagation and emission of light. These nanostructures are well-known for their ability to control the emission and propagation of light. The opals have a periodic variation of the refractive index (see Figure 1) that ensures that a certain color of light is forbidden to exist inside the opal. The light cannot enter the opal as it is reflected, which is called a gap (see Figure 1). In an analogy to semiconductors, such an effect is called a “photonic band gap”. Photonic gaps are at the basis of tiny on-chip light sources and lasers, efficient solar cells, invisibility cloaks, and devices to process optical information.

The Twente team changed the index of refraction of the voids in a photonic crystal by substituting the air by a vapor of atoms with a strong resonance, as shown in Figure 1. The contrast of the refractive index between the vapor and the opal’s silica nano­spheres was effectively used as a probe. The density of the cesium vapor was greatly varied by changing the temperature in the cell up to 420 K. At the same time, the photonic gap of the opal shifted relative to the atomic resonance due to a slow chemical reaction between the opal’s backbone material (silica) and the cesium.

On resonance, light excites an atom to a higher state and subsequently the atom reemits the light. Hence, an atom behaves like a little cavity that stores light. Simultaneously the index of refraction changes strongly for colors near resonance. For slightly longer wavelengths the index of refraction is high, on resonance it is close to one, and slightly shorter wavelengths it can even decrease below one. This effect of the cesium atoms is clearly visible in the reflectivity spectra, shown in Figure 2 [not included here], as a sharp increase and decrease of the reflectivity near the atomic resonance. Intriguingly, the characteristic peak-and-trough behavior of atoms (seen at 370 K) was turned upside down at the highest temperature (420 K), where the ce­sium reso­nance was on the red side of the opal’s stopgap.

In nanophotonics, many efforts are currently being devoted to create arrays of nanoresonators in photonic crystals, for exquisite optical signal control on a chip. Unfortunately, however, there is a major challenge in engineering high-quality pho­tonic resonators: they are all different due to inevitable fabrication variations. Hence, it is difficult to tune every resonator in sync. “Our atoms in the opal may be consid­ered as the equivalent of an carefully engineered array of nano-resonators” explains Willem Vos, “Nature takes care that all resonators are all exactly the same. Our hy­brid system solves the variability problem and could perhaps be used to make pho­tonic memories, sensors or switches that are naturally tuned.” And leading Spanish theorist Javier Garcia de Abajo (ICFO) enthuses: “This is a fine and exciting piece of work, initiating the study of atomic resonances with photonic modes in a genuinely new fashion, and suggesting many exciting possibilities, for example through the extension of this study towards combinations with metal nanoplasmonics.”

Here’s a link to and a citation for the paper published in Physical Review B,

Nanophotonic hybridization of narrow atomic cesium resonances and photonic stop gaps of opaline nanostructures by Philip J. Harding, Pepijn W. H. Pinkse, Allard P. Mosk, and Willem L. Vos. Phys. Rev. B 91, 045123 – Published 20 January 2015 DOI: http://dx.doi.org/10.1103/PhysRevB.91.045123

This paper is behind a paywall but there is an earlier iteration of the paper available on the open access arXiv.org website operated by Cornell University,

Nanophotonic hybridization of narrow atomic cesium resonances and photonic stop gaps of opaline nanostructures by Philip J. Harding, Pepijn W.H. Pinkse, Allard P. Mosk, Willem L. Vos. (Submitted on 11 Sep 2014) arXiv:1409.3417

As I understand it, the arXiv.org website is intended to open up access to research and to offer an informal peer review process.

Finally, for anyone who’s nostalgic or perhaps has never heard Diana Ross sing ‘Upside Down’,

Atlantic Canada’s Lamda Guard signs deal to test nanocomposite windshield film with Airbus

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This story comes from Nova Scotia although you wouldn’t know it if you’d only read the June 5, 2014 news item on Azonano,

Lamda Guard, a company based in Atlantic Canada, has signed an agreement with leading aircraft manufacturer Airbus to test a breakthrough innovation designed to deflect unwanted bright light or laser sources from impacting jetliner flight paths, and causing pilot disorientation or injury.

A June 4, 2014 news release (either from Lamda Guard.com or MTI [metamaterial.com]; Note: More about the multiple webspaces later] and there’s a PDF version here), which originated the news item, provides a little more information about the technology and the perspectives from various stakeholders

Lamda Guard’s innovative thin films utilize metamaterial technology on cockpit windscreens to selectively block and control light coming from any angle even at the highest power levels. “Today marks a milestone in optical applications of nano-composites,” said George Palikaras, President and CEO of Lamda Guard. “Through our collaboration with Airbus we are working to introduce our metamaterial technology, for the first time, as a solution to laser interference in the aviation industry.” The announcement today comes within weeks of the release of an FBI [US Federal Bureau of Investigation] report citing 3,960 aircraft laser strikes in the US in 2013 according to the Federal Aviation Authority (FAA).

Senior Vice President of Innovation Yann Barbaux stated: “At Airbus, we are always on the lookout for new ideas coming from innovative SMEs [small to medium enterprises], such as Lamda Guard. We are very pleased to explore together the potential application of this solution to our aircraft, for the benefit of our customers.”

Over the past year Lamda Guard has been working with the research community at the University of Moncton and the University of New Brunswick, as well as stakeholders, investors and funders to highlight the benefits of nano-composites. The Atlantic Canada Opportunities Agency (ACOA) in particular has played an important role in Lamda Guard’s research and development efforts. In 2012, ACOA assisted Lamda Guard with technology commercialization and recently upgraded its contribution to $500,000 to further assist the company in developing and manufacturing its products for the aviation industry.

…

The Lamda Guard Airbus partnership marks the first time an optical metamaterial nano-composite has been applied on a large-scale surface.

I tried to find more information about the technology and tracked down this tiny bit, from the What are MetaMaterials? webpage on the MTI website,

A metamaterial typically consists of a multitude of structured unit cells that are comprised of multiple individual elements, which are referred to as meta-atoms. The individual elements are assembled from conventional microscopic materials such as metals and/or plastics, which are arranged in periodic patterns.

…

MTI’s precisely designed structures are developed with proprietary algorithms, producing a new generation of optical products that are built in state-of-the-art thin film nano-fabrication labs. MTI’s proprietary software accurately predicts the desired design pattern to generate a unique material that meets customer specifications. MTI’s sleek designs mean manufacturers can reduce their cost of materials significantly while increasing performance, e.g. by increasing the light output of an LED bulb or increasing the absorption of light in a solar panel.

Multiple webspaces and presences

While Lamda Guard has a .com presence, you will find yourself on the metamaterial.com website in the Lamda Guard webspace (I suppose you could also call it a subsite) once you start clicking for more information.  In fact, MTI owns three Lamda companies as per this description from the Our Company webpage on the MTI (metamaterial.com) website (Note: Links have been removed),

MTI is an advanced materials and systems engineering company developing and commercializing innovative optical solutions. The company’s core team has over 200 years of combined experience at the forefront of the design and implementation of metamaterials, making MTI a pioneer in bridging the gap between the theoretical and the possible.

MTI specializes in metamaterials, nanotechnology, theoretical and computational electromagnetics. The company’s in-house expertise enables the rapid development of a wide array of metamaterial applications, covering a diverse range of markets.

MTI’s technologies are adaptable and can be custom-designed to suit an industry manufacturer’s specifications allowing for scalability and rapid prototyping with minimum overheads. MTI provides access to world class nano-composite research and development, including specialty, as well as customized, products and licensing of its proprietary solutions to customers ranging from government to private companies.

MTI has three wholly owned subsidiaries:

Lamda Guard Inc. which develops advanced filters to block out selected parts of the light spectrum, protecting the eyes from lasers or other sources of hazardous light.

Lamda Solar Inc. products increase the efficiency of solar panel cells by absorbing more light.

Lamda Lux Inc. technology increases the delivered lumens and reduces the cost of thermal management of LED lighting.

Interestingly, the Lamda Guard Management team‘s (in the Lamda Guard webspace) Chief Science Officer, Dr. Themos Kallos, and Chief Intellectual Property Officer, Dr. Quinton Fivelman, both appear to reside in the UK (assuming I looked at the correct LinkedIn profiles).  Coincidentally, MTI’s contact page lists the company’s headquarters as being in Nova Scotia but Sales, Research and Development would seem to be located in the UK.

Presumably, this company is maximizing its access to government grants and tax incentives in both the UK and Canada. The deal with the Airbus suggests that this has been a successful strategy possibly leading to commercialized technology and, hopefully, jobs.

Smart ‘curtains’ from the University of California at Berkeley

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There’s a weirdly fascinating video that accompanies this research into light-activation and carbon nanotubes,

A Jan. 10, 2014 news item on Nanowerk provides an explanation,

A research team led by Ali Javey, associate professor of electrical engineering and computer sciences [University of California at Berkeley], layered carbon nanotubes – atom-thick rolls of carbon – onto a plastic polycarbonate membrane to create a material that moves quickly in response to light. Within fractions of a second, the nanotubes absorb light, convert it into heat and transfer the heat to the polycarbonate membrane’s surface. The plastic expands in response to the heat, while the nanotube layer does not, causing the two-layered material to bend.

The Jan. 9, 2014 University of California at Berkeley research brief by Sarah Yang, which originated the news item, provides some perspective from lead researcher Javey and a few more details about the research,

“The advantages of this new class of photo-reactive actuator is that it is very easy to make, and it is very sensitive to low-intensity light,” said Javey, who is also a faculty scientist at the Lawrence Berkeley National Lab. “The light from a flashlight is enough to generate a response.”

The researchers described their experiments in a paper published this week in the journal Nature Communications. They were able to tweak the size and chirality – referring to the left or right direction of twist – of the nanotubes to make the material react to different wavelengths of light. The swaths of material they created, dubbed “smart curtains,” could bend or straighten in response to the flick of a light switch.

“We envision these in future smart, energy-efficient buildings,” said Javey. “Curtains made of this material could automatically open or close during the day.”  [emphasis mine]

Other potential applications include light-driven motors and robotics that move toward or away from light, the researchers said.

Here’s a link to and a citation for the paper,

Photoactuators and motors based on carbon nanotubes with selective chirality distributions by Xiaobo Zhang, Zhibin Yu, Chuan Wang, David Zarrouk, Jung-Woo Ted Seo, Jim C. Cheng, Austin D. Buchan, Kuniharu Takei, Yang Zhao, Joel W. Ager, Junjun Zhang, Mark Hettick, Mark C. Hersam, Albert P. Pisano, Ronald S. Fearing, & Ali Javey. Nature Communications 5, Article number: 2983 doi:10.1038/ncomms3983 Published 07 January 2014

The earlier reference to energy-efficient buildings suggests that this work with light-activated curtains is another variation of a ‘smart’ window’ and bears some resemblance to Boris Lamontagne’s (Canada National Research Council) work with curling electrodes which act as blinds in his version of smart glass as per my .Sept. 16, 2011 posting.

Ali Javey has been mentioned here before in a Sept. 15, 2010 post concerning nanotechnology-enabled robot skin.