Category Archives: nanophotonics

Data transmisstion at 1.44 terabits per second

It’s not only the amount of data we have which is increasing but the amount of data we want to transmit from one place to another. An April 14, 2014 news item on ScienceDaily describes a new technique designed to increase data transmission rates,

Miniaturized optical frequency comb sources allow for transmission of data streams of several terabits per second over hundreds of kilometers — this has now been demonstrated by researchers of Karlsruhe Institute of Technology (KIT) and the Swiss École Polytechnique Fédérale de Lausanne (EPFL) in a experiment presented in the journal Nature Photonics. The results may contribute to accelerating data transmission in large computing centers and worldwide communication networks.

In the study presented in Nature Photonics, the scientists of KIT, together with their EPFL colleagues, applied a miniaturized frequency comb as optical source. They reached a data rate of 1.44 terabits per second and the data was transmitted over a distance of 300 km. This corresponds to a data volume of more than 100 million telephone calls or up to 500,000 high-definition (HD) videos. For the first time, the study shows that miniaturized optical frequency comb sources are suited for coherent data transmission in the terabit range.

The April (?) 2014 KIT news release, which originated the news item, describes some of the current transmission technology’s constraints,

The amount of data generated and transmitted worldwide is growing continuously. With the help of light, data can be transmitted rapidly and efficiently. Optical communication is based on glass fibers, through which optical signals can be transmitted over large distances with hardly any losses. So-called wavelength division multiplexing (WDM) techniques allow for the transmission of several data channels independently of each other on a single optical fiber, thereby enabling extremely high data rates. For this purpose, the information is encoded on laser light of different wavelengths, i.e. different colors. However, scalability of such systems is limited, as presently an individual laser is required for each transmission channel. In addition, it is difficult to stabilize the wavelengths of these lasers, which requires additional spectral guard bands between the data channels to prevent crosstalk.

The news release goes on to further describe the new technology using ‘combs’,

Optical frequency combs, for the development of which John Hall and Theodor W. Hänsch received the 2005 Nobel Prize in Physics, consist of many densely spaced spectral lines, the distances of which are identical and exactly known. So far, frequency combs have been used mainly for highly precise optical atomic clocks or optical rulers measuring optical frequencies with utmost precision. However, conventional frequency comb sources are bulky and costly devices and hence not very well suited for use in data transmission. Moreover, spacing of the spectral lines in conventional frequency combs often is too small and does not correspond to the channel spacing used in optical communications, which is typically larger than 20 GHz.

In their joint experiment, the researchers of KIT and the EPFL have now demonstrated that integrated optical frequency comb sources with large line spacings can be realized on photonic chips and applied for the transmission of large data volumes. For this purpose, they use an optical microresonator made of silicon nitride, into which laser light is coupled via a waveguide and stored for a long time. “Due to the high light intensity in the resonator, the so-called Kerr effect can be exploited to produce a multitude of spectral lines from a single continuous-wave laser beam, hence forming a frequency comb,” explains Jörg Pfeifle, who performed the transmission experiment at KIT. This method to generate these so-called Kerr frequency combs was discovered by Tobias Kippenberg, EPFL, in 2007. Kerr combs are characterized by a large optical bandwidth and can feature line spacings that perfectly meet the requirements of data transmission. The underlying microresonators are produced with the help of complex nanofabrication methods by the EPFL Center of Micronanotechnology. “We are among the few university research groups that are able to produce such samples,” comments Kippenberg. Work at EPFL was funded by the Swiss program “NCCR Nanotera” and the European Space Agency [ESA].

Scientists of KIT’s Institute of Photonics and Quantum Electronics (IPQ) and Institute of Microstructure Technology (IMT) are the first to use such Kerr frequency combs for high-speed data transmission. “The use of Kerr combs might revolutionize communication within data centers, where highly compact transmission systems of high capacity are required most urgently,” Christian Koos says.

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

Coherent terabit communications with microresonator Kerr frequency combs by Joerg Pfeifle, Victor Brasch, Matthias Lauermann, Yimin Yu, Daniel Wegner, Tobias Herr, Klaus Hartinger, Philipp Schindler, Jingshi Li, David Hillerkuss, Rene Schmogrow, Claudius Weimann, Ronald Holzwarth, Wolfgang Freude, Juerg Leuthold, Tobias J. Kippenberg, & Christian Koos. Nature Photonics (2014) doi:10.1038/nphoton.2014.57 Published online 13 April 2014

This paper is behind a paywall.

Seeing quantum entanglement and using quantum entanglement to build a wormhole

Kudos to the team from the Vienna Center for Quantum Science and Technology for the great musical accompaniment on their video showing quantum entanglement in real time,

A Dec. 4, 2013 news item on Nanowerk provides more details,

Einstein called quantum entanglement “spooky action at a distance”. Now, a team from the Vienna Center for Quantum Science and Technology has reported imaging of entanglement events where the influence of the measurement of one particle on its distant partner particle is directly visible (“Real-Time Imaging of Quantum Entanglement”).

The Dec. 4, 2013 Andor news release, which originated the news item, gives more details about the team’s work and about the Andor camera which enabled it,

The key to their success is the Andor iStar 334T Intensified CCD (ICCD) camera, which is capable of very fast (nanosecond) and precise (picosecond) optical gating speeds. Unlike the relatively long microsecond exposure times of CCD and EMCCD cameras which inhibits their usefulness in ultra-high-speed imaging, this supreme level of temporal resolution made it possible for the team to perform a real-time coincidence imaging of entanglement for the first time.

“The Andor iStar ICCD camera is fast enough, and sensitive enough, to image in real-time the effect of the measurement of one photon on its entangled partner,” says Robert Fickler of the Institute for Quantum Optics and Quantum Information. “Using ICCD cameras to evaluate the number of photons from a registered intensity within a given region opens up new experimental possibilities to determine more efficiently the structure and properties of spatial modes from only single intensity images. Our results suggest that triggered ICCD cameras will advance quantum optics and quantum information experiments where complex structures of single photons need to be investigated with high spatio-temporal resolution.”

According to Antoine Varagnat, Product Specialist at Andor, “The experiment produces pairs of photons which are entangled so as to have opposite polarisations. For instance, if one of a pair has horizontal polarisation, the other has vertical, and so on. The first photon is sent to polarising glass that transmits photons of one angle only, followed by a detector to register photons which make it through the glass. The other photon is delayed by a fibre, then its entangled property is coherently transferred from the polarisation to the spatial mode and afterwards brought to the high-speed, ultra-sensitive iStar camera.

“The use of the ICCD camera allowed the team to demonstrate the high flexibility of the setup in creating any desired spatial-mode entanglement. Their results suggest that visual imaging in quantum optics not only provides a better intuitive understanding of entanglement but will also improve applications of quantum science,” concludes Varagnat.

Research into quantum entanglement was instigated in 1935 by Albert Einstein, Boris Podolsky and Nathan Rosen, in a paper critiquing quantum mechanics. Erwin Schrödinger also wrote several papers shortly afterwards. Although these first studies focused on the counterintuitive properties of entanglement with the aim of criticising quantum mechanics, entanglement was eventually verified experimentally and recognised as a valid, fundamental feature of quantum mechanics. Nowadays, the focus of the research has changed to its utilization in communications and computation, and has been used to realise quantum teleportation experimentally.

The team’s work is chronicled in this study,

Real-Time Imaging of Quantum Entanglement by Robert Fickler, Mario Krenn, Radek Lapkiewicz, Sven Ramelow & Anton Zeilinger. Scientific Reports 3, Article number: 1914 doi:10.1038/srep01914 Published 29 May 2013

This is an open access paper.

Meanwhile, researchers at the University of Washington (Seattle, Washington state) explore the quantum entanglement phenomenon with an eye to wormholes (from the De.c 3, 2013 University of Washington news release [also on EurekAlter]),

Quantum entanglement, a perplexing phenomenon of quantum mechanics that Albert Einstein once referred to as “spooky action at a distance,” could be even spookier than Einstein perceived.

Physicists at the University of Washington and Stony Brook University in New York believe the phenomenon might be intrinsically linked with wormholes, hypothetical features of space-time that in popular science fiction can provide a much-faster-than-light shortcut from one part of the universe to another.

But here’s the catch: One couldn’t actually travel, or even communicate, through these wormholes, said Andreas Karch, a UW physics professor.

Quantum entanglement occurs when a pair or a group of particles interact in ways that dictate that each particle’s behavior is relative to the behavior of the others. In a pair of entangled particles, if one particle is observed to have a specific spin, for example, the other particle observed at the same time will have the opposite spin.

The “spooky” part is that, as research has confirmed, the relationship holds true no matter how far apart the particles are – across the room or across several galaxies. If the behavior of one particle changes, the behavior of both entangled particles changes simultaneously, no matter how far away they are.

Recent research indicated that the characteristics of a wormhole are the same as if two black holes were entangled, then pulled apart. Even if the black holes were on opposite sides of the universe, the wormhole would connect them.

Black holes, which can be as small as a single atom or many times larger than the sun, exist throughout the universe, but their gravitational pull is so strong that not even light can escape from them.

If two black holes were entangled, Karch said, a person outside the opening of one would not be able to see or communicate with someone just outside the opening of the other.

“The way you can communicate with each other is if you jump into your black hole, then the other person must jump into his black hole, and the interior world would be the same,” he said.

The work demonstrates an equivalence between quantum mechanics, which deals with physical phenomena at very tiny scales, and classical geometry – “two different mathematical machineries to go after the same physical process,” Karch said. The result is a tool scientists can use to develop broader understanding of entangled quantum systems.

“We’ve just followed well-established rules people have known for 15 years and asked ourselves, ‘What is the consequence of quantum entanglement?’”

The researchers have provided an illustration, which looks more like a ‘smiley face’ to me. Are wormholes smiley faces in space,

Alan Stonebraker/American Physical Society This illustration demonstrates a wormhole connecting two black holes.

Alan Stonebraker/American Physical Society
This illustration demonstrates a wormhole connecting two black holes.

Here’s a link to and a citation for the research paper on quantum entanglement and wormholes,

Holographic Dual of an Einstein-Podolsky-Rosen Pair has a Wormhole by Kristan Jensen and Andreas Karch. Phys. Rev. Lett. 111, 211602 (2013) [5 pages] Published 20 November 2013

This paper is behind a paywall.

ETA Dec. 11, 2013: There’s a news item today, Dec. 11, 2013, on Nanowerk which casts an interesting light on Andor,

Nanotechnology specialist Oxford Instruments is to take over Belfast-based scientific camera maker Andor in a £176million deal.
The Andor board last night agreed a 525p a share offer, giving a 31 per cent premium over the closing price before Oxford’s initial 500p a share pitch in November.

The two companies have been in talks since July [2013].

Shares in Andor rose 10p to 515p and Oxford Instruments gained 8p to 1566p.

It looks like their Dec. 4, 2013 news release was a leadup to this business news.

Dye your carbon nantubes for better resolution

A team at the Université de Montréal has developed a technique for making nanoscale objects more easily seen. From a Dec. 2, 2013 news item on Nanowerk (Note: A link has been removed),

Richard Martel and his research team at the Department of Chemistry of the Université de Montréal have discovered a method to improve detection of the infinitely small. Their discovery is presented in the November 24 online edition of the journal Nature Photonics (“Giant Raman scattering from J-aggregated dyes inside carbon nanotubes for multispectral imaging”).

“Raman scattering provides information on the ways molecules vibrate, which is equivalent to taking their fingerprint. It’s a bit like a bar code,” said the internationally renowned professor. “Raman signals are specific for each molecule and thus useful in identifying these molecules.”

The discovery by Martel’s team is that Raman scattering of dye-nanotube particles is so large that a single particle of this type can be located and identified. All one needs is an optical scanner capable of detecting this particle, much like a fingerprint.

I haven’t been able to track down the English language version of the Dec. 2, 2013 Université de Montréal news release but here are some excerpts from the French language version by Dominique Nancy,

Grâce à l’alignement de molécules de colorants encapsulées dans un nanotube de carbone, les chercheurs ont réussi à amplifier le signal Raman jusqu’ici pas assez puissant de ces colorants pour permettre leur détection. L’article présente les données expérimentales d’une diffusion extraordinaire de lumière visible sur une particule de taille nanométrique.

«La diffusion Raman contient de l’information sur les modes de vibration des molécules, ce qui équivaut à relever leurs empreintes digitales. C’est un peu comme un code à barres, explique le professeur de renommée internationale. Le signal Raman est propre à chaque molécule et donc très utile pour la repérer.»

Le mode de diffusion Raman est un phénomène optique mis au jour en 1928 par le physicien Chandrashekhara Venkata Râman. L’effet consiste en la diffusion inélastique d’un photon, c’est-à-dire le phénomène physique par lequel un milieu peut modifier la fréquence de la lumière qui y circule. ….


Mais jusqu’à ce jour, le signal Raman des molécules était trop faible pour répondre efficacement aux besoins en imagerie optique. Les chercheurs avaient donc recours à d’autres techniques optiques plus sensibles mais moins précises, car elles ne possèdent pas de «code à barres». «Il est toutefois possible techniquement de voir les signaux Raman avec un spectromètre lorsque la concentration des molécules est assez élevée, indique M. Martel. Mais cela limite les applications du Raman.»


Composé d’une centaine de molécules colorées et alignées dans le cylindre, le nanotraceur est 50 000 fois plus petit qu’un cheveu. Il mesure environ un nanomètre de diamètre et 500 de long. Et pourtant les particules colorées encapsulées dans le nanotube de carbone donnent un signal Raman un million de fois plus intense que celui des autres molécules autour de l’objet.

On peut aussi imaginer un douanier qui scannerait notre passeport avec un mode Raman multispectral (aux signaux multiples). Ces nanotraceurs pourraient également être utilisés dans les encres des billets de banque, rendant la contrefaçon presque impossible.

La beauté de la chose, affirme Richard Martel, c’est que le phénomène est général et plusieurs types de colorants peuvent servir à la fabrication des nanotraceurs, dont les «codes à barres» sont tous différents. «On a fabriqué jusqu’ici plus de 10 traceurs et il semble qu’il n’y a pas de limite, dit-il. On pourrait donc en principe créer autant de nanotraceurs qu’il y a de bactéries et utiliser ce principe pour les déceler avec un microscope fonctionnant en mode Raman.»

As I have noted many times here, my linguistic skills are shaky but here’s my overview:

Due to the colouring agent researchers have added to the carbon nanotubes in the experiement, it is possible to amplify the Ramen signal allowing for an extraordinary resolution making nanoscale objects optically visible.

With the dyed carbon nanotubes, the new technique offers the equivalent of a unique digital fingerprint or, Martel also describes it, as a unique bar code for nanoscale objects. Standard Raman technique can be used to detect nanoscale objects when there’s a high concentration but is not not powerful enough to optically detect nanoscale objects in lower concentrations or with any precision, i.e., the ability to detect a unique ‘fingerprint’ or ‘bar code’.

The nanotracer, the dyed carbon nanotube, is 1/50,000 the diameter of a human hair and can measure object of approximately 500 nm in diameter.

Martel sees a number of applications for this new technique include biomedical applications.

You may want to take a look at the news item on Nanowerk for a better and more complete translation.

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

Giant Raman scattering from J-aggregated dyes inside carbon nanotubes for multispectral imaging by E. Gaufrès, N. Y.-Wa Tang, F. Lapointe, J. Cabana, M.-A. Nadon, N. Cottenye, F. Raymond, T. Szkopek, & R. Martel. Nature Photonics (2013) doi:10.1038/nphoton.2013.309 Published online 24 November 2013

This article is behind a paywall.

Bejweled and bedazzled but not bewitched, bothered, or bewildered at Northwestern University

When discussing DNA (deoxyribonucleic acid) one doesn’t usually expect to encounter gems as one does in a Nov. 28, 2013 news item on Azonano,

Nature builds flawless diamonds, sapphires and other gems. Now a Northwestern University [located in Chicago, Illinois, US] research team is the first to build near-perfect single crystals out of nanoparticles and DNA, using the same structure favored by nature.

The Nov. 27, 2013 Northwestern University news release by Megan Fellman (also on EurekAlert), which originated the news item,, explains why single crystals are of such interest,

“Single crystals are the backbone of many things we rely on — diamonds for beauty as well as industrial applications, sapphires for lasers and silicon for electronics,” said nanoscientist Chad A. Mirkin. “The precise placement of atoms within a well-defined lattice defines these high-quality crystals.

“Now we can do the same with nanomaterials and DNA, the blueprint of life,” Mirkin said. “Our method could lead to novel technologies and even enable new industries, much as the ability to grow silicon in perfect crystalline arrangements made possible the multibillion-dollar semiconductor industry.”

His research group developed the “recipe” for using nanomaterials as atoms, DNA as bonds and a little heat to form tiny crystals. This single-crystal recipe builds on superlattice techniques Mirkin’s lab has been developing for nearly two decades.

(I wrote about Mirkin’s nanoparticle DNA work in the context of his proposed periodic table of modified nucleic acid nanoparticles in a July 5, 2013 posting.) The news release goes on to describe Mirkin’s most recent work,

In this recent work, Mirkin, an experimentalist, teamed up with Monica Olvera de la Cruz, a theoretician, to evaluate the new technique and develop an understanding of it. Given a set of nanoparticles and a specific type of DNA, Olvera de la Cruz showed they can accurately predict the 3-D structure, or crystal shape, into which the disordered components will self-assemble.

The general set of instructions gives researchers unprecedented control over the type and shape of crystals they can build. The Northwestern team worked with gold nanoparticles, but the recipe can be applied to a variety of materials, with potential applications in the fields of materials science, photonics, electronics and catalysis.

A single crystal has order: its crystal lattice is continuous and unbroken throughout. The absence of defects in the material can give these crystals unique mechanical, optical and electrical properties, making them very desirable.

In the Northwestern study, strands of complementary DNA act as bonds between disordered gold nanoparticles, transforming them into an orderly crystal. The researchers determined that the ratio of the DNA linker’s length to the size of the nanoparticle is critical.

“If you get the right ratio it makes a perfect crystal — isn’t that fun?” said Olvera de la Cruz, who also is a professor of chemistry in the Weinberg College of Arts and Sciences. “That’s the fascinating thing, that you have to have the right ratio. We are learning so many rules for calculating things that other people cannot compute in atoms, in atomic crystals.”

The ratio affects the energy of the faces of the crystals, which determines the final crystal shape. Ratios that don’t follow the recipe lead to large fluctuations in energy and result in a sphere, not a faceted crystal, she explained. With the correct ratio, the energies fluctuate less and result in a crystal every time.

“Imagine having a million balls of two colors, some red, some blue, in a container, and you try shaking them until you get alternating red and blue balls,” Mirkin explained. “It will never happen.

“But if you attach DNA that is complementary to nanoparticles — the red has one kind of DNA, say, the blue its complement — and now you shake, or in our case, just stir in water, all the particles will find one another and link together,” he said. “They beautifully assemble into a three-dimensional crystal that we predicted computationally and realized experimentally.”

To achieve a self-assembling single crystal in the lab, the research team reports taking two sets of gold nanoparticles outfitted with complementary DNA linker strands. Working with approximately 1 million nanoparticles in water, they heated the solution to a temperature just above the DNA linkers’ melting point and then slowly cooled the solution to room temperature, which took two or three days.

The very slow cooling process encouraged the single-stranded DNA to find its complement, resulting in a high-quality single crystal approximately three microns wide. “The process gives the system enough time and energy for all the particles to arrange themselves and find the spots they should be in,” Mirkin said.

The researchers determined that the length of DNA connected to each gold nanoparticle can’t be much longer than the size of the nanoparticle. In the study, the gold nanoparticles varied from five to 20 nanometers in diameter; for each, the DNA length that led to crystal formation was about 18 base pairs and six single-base “sticky ends.”

“There’s no reason we can’t grow extraordinarily large single crystals in the future using modifications of our technique,” said Mirkin, who also is a professor of medicine, chemical and biological engineering, biomedical engineering and materials science and engineering and director of Northwestern’s International Institute for Nanotechnology.

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

DNA-mediated nanoparticle crystallization into Wulff polyhedra by Evelyn Auyeung, Ting I. N. G. Li, Andrew J. Senesi, Abrin L. Schmucker, Bridget C. Pals, Monica Olvera de la Cruz, & Chad A. Mirkin. Nature (2013) doi:10.1038/nature12739 Published online 27 November 2013

This article is behind a paywall.

Points to anyone who recognized the song title (Bewitched, Bothered and Bewildered) embedded in the head for this posting.

New book ‘Wonder of Nanotechnology’ explores optical and electronic systems

Nature is nano.

Nature starts with the atom, the building block of all matter, and works hand-in-hand with her partner the photon, the piece of light that communicates energy from one atom to another.When nature binds atoms together or creates physical structures in the micro- and nano-range, the combinations interact differently with light, providing nature with a rich palette of colors to decorate the world around us,while also giving rise to the functional complexity of nature.The wings of a butterfly, the feather of a peacock, the sheen of a pearl—all of these are examples of nature’s photonic crystals: nanostructured arrangements of atoms that capture and recast the colors of the rainbow with iridescent beauty. These diverse combinations of microstructures and atoms in molecules, crystals, proteins, and cells on the nanoscale eventually give rise to ourselves, sentient beings, who, in turn, strive to explain the natural world that we see around us.. (from the Preface for the Wonder of Nanotechnology)

The Nov. 21, 2013 SPIE, the international society for optics and photonics news release touting the book is a little more restrained than the dramatic ‘Nature is nano’,,

BELLINGHAM, Washington, USA – Nanotechnology research has progressed into quantum-level systems where electrons, photonics, and even thermal properties can be engineered, enabling new structures and materials with which to create ever-shrinking, ever-faster electronics. The Wonder of Nanotechnology: Quantum Optoelectronic Devices and Applications, edited by Manijeh Razeghi and Nobel Laureates Leo Esaki and Klaus von Klitzing, focuses on the application of nanotechnology to modern semiconductor optoelectronic devices The book is published by SPIE, the international society of optics and photonics.

The volume is a compilation of research papers from the International Conference on Infrared Optoelectronics at Northwestern University’s Center for Quantum Devices in September 2012, developed into chapters representing state-of-the-art research in infrared materials and devices.

“Advances in material science at the nanometer scale are opening new doors in the area of optics and electronics. The ability to manipulate atoms and photons, and fabricate new material structures offers opportunities to realize new emitters, detectors, optics, ever-shrinking electronics, and integration of optics and electronics,” writes Nibir Dhar, program manager with Defense Advanced Research Project Agency (DARPA), in an essay in the book. “Imaging technology has the opportunity to leverage these developments to produce new products for military, industrial, medical, security, and other consumer applications.”

The editors of Wonder of Nanotechnology are:

  • Manijeh Razeghi, director of the Center for Quantum Devices at Northwestern University and one of the leading scientists in the field of semiconductor science and technology. Razeghi pioneered nanometer-scale architectures in semiconductor technology, and her research in quantum materials has culminated in various technologies such as type-II strained-layer superlattice infrared detectors, lasers, and terahertz technology. Her current interest is in nanoscale optoelectronic quantum devices.
  • Leo Esaki, who shared the 1973 Nobel Prize in Physics for his discovery of the phenomenon of electron tunneling while working at Tokyo Tsushin Kogyo (now known as Sony). He is known for his invention of the Esaki diode, which exploited that phenomenon. He also pioneered the development of the semiconductor superlattice while at IBM, and is president of the Yokohama College of Pharmacy in Japan.
  • Klaus von Klitzing, director of the Max Planck Institute for Solid State Research in Germany. Von Klitzing was awarded the 1985 Nobel Prize in Physics for his discovery of the integer quantum Hall effect. His current research focuses on the properties of low-dimensional electronic systems, typically in low temperatures and in high magnetic fields.

“The chapters in this book bear witness to how far we have come since the invention of manmade semiconductor superlattices in 1969,” Esaki writes in the book’s foreword. “I look back with wonder at all of the exciting developments of the last 44 years and can only imagine where the future will take this technology and what exciting discoveries await.”

The book’s editors also address the inspiration of nature in studying nanoscale structures, and how the human ability to control material composition on the nanometer scale is what allows us to achieve technological goals transcending the properties of naturally occurring materials.

“The wings of a butterfly, the feather of a peacock, the sheen of a pearl — all of these are examples of nature’s photonic crystals: nanostructured arrangements of atoms that capture and recast the colors of the rainbow with iridescent beauty,” von Klitzing writes in the book’s preface. “As our tools to manipulate matter reach ever smaller length scales, we, too, are able to join in the game of discovery in the nano-world — a game that nature has long since mastered.”

Notable chapters include:

  • “Advances in High-Power Quantum Cascade Lasers and Applications” by Arkadiy Lyakh, Richard Maulini, Alexei Tsekoun, and Boris Tadjikov (Pranalytica, Inc.), and CO2-laser inventor Kumar Patel (Pranalytica, Inc., and University of California Los Angeles)
  • “Type-II Superlattices: Status and Trends” by Elena Plis and Sanjay Krishna (Center for High-Technology Materials, University of New Mexico)
  • “Quantum Dots for Infrared Focal Plane Arrays Grown by MOCVD” by Manijeh Razeghi and Stanley Tsao (Center for Quantum Devices, Northwestern University)
  • “Quantum-Dot Biosensors using Fluorescence Resonance Energy Transfer (FRET)” by James Garland and Dinakar Ramadurai (Episensors, Inc., and Sivananthan Laboratories, Inc.) and Siva Sivananthan (Sivananthan Laboratories, Inc., and University of Illinois)
  • “Nanostructured Electrode Interfaces for Energy Applications” by Palash Gangopadhyay, Kaushik Balakrishnan, and Nasser Peyghambarian (College of Optical Sciences, University of Arizona)

You can go here to purchase the book.

Australians inspired by Lycurgus Cup

The Lycurgus Cup is one of the great artistic achievements in history and there’s a nanotechnology twist to this art work created in the 4th century CE (or AD). From the Nov. 21, 2013 news item on Nanowerk,

A 1700-year-old Roman glass cup is inspiring University of Adelaide [Australia] researchers in their search for new ways to exploit nanoparticles and their interactions with light.

Researchers in the University’s Institute for Photonics and Advanced Sensing (IPAS) are investigating how to best embed nanoparticles in glass – instilling the glass with the properties of the nanoparticles it contains.

Before going further with this latest work at the University of Adelaide, here’s an excerpt from my Sept. 21, 2010 posting where I burbled on about the best of piece of writing I’ve seen about the Lycurgus Cup (held in the British Museum),

The *History of the Ancient World website (as Nov. 21, 2013 the link has been changed to the Université de Strasbourg,, Matière Condensée et Nanophysique website) recently featured a 2007 article about the Lycurgus Cup by Ian Freestone, Nigel Meeks, Margaret Sax and Catherine Higgitt for the Gold Bulletin, Vol. 40:4 (2007),

The Lycurgus Cup represents one of the outstanding achievements of the ancient glass industry. This late Roman cut glass vessel is extraordinary in several respects, firstly in the method of fabrication and the exceptional workmanship involved and secondly in terms of the unusual optical effects displayed by the glass.

The Lycurgus Cup is one of a class of Roman vessels known as cage cups or diatreta, where the decoration is in openwork which stands proud from the body of the vessel, to which it is linked by shanks or bridges Typically these openwork “cages” comprise a lattice of linked circles, but a small number have figurative designs, although none of these is as elaborate or as well preserved as the Lycurgus Cup. Cage cups are generally dated to the fourth century A.D. and have been found across the Roman Empire, but the number recovered is small, and probably only in the region of 50-100 examples are known. They are among the most technically sophisticated glass objects produced before the modern era.

Here’s what it looks like,

The Lycurgus Cup 1958,1202.1 in reflected light. Scene showing Lycurgus being enmeshed by Ambrosia, now transformed into a vine-shoot. Department of Prehistory and Europe, The British Museum. Height: 16.5 cm (with modern metal mounts), diameter: 13.2 cm. © The Trustees of the British Museum

The Lycurgus Cup 1958,1202.1 in reflected light. Scene showing Lycurgus being enmeshed by Ambrosia, now transformed into a vine-shoot. Department of Prehistory and Europe, The British Museum. Height: 16.5 cm (with modern metal mounts), diameter: 13.2 cm. © The Trustees of the British Museum

And this, too, is the one and only Lycurgus Cup,

The Lycurgus Cup 1958,1202.1 in transmitted light. Scene showing Lycurgus being enmeshed by Ambrosia, now transformed into a vine-shoot. Department of Prehistory and Europe, The British Museum. Height: 16.5 cm (with modern metal mounts), diameter: 13.2 cm. © The Trustees of the British Museum

The Lycurgus Cup 1958,1202.1 in transmitted light. Scene showing Lycurgus being enmeshed by Ambrosia, now transformed into a vine-shoot. Department of Prehistory and Europe, The British Museum. Height: 16.5 cm (with modern metal mounts), diameter: 13.2 cm. © The Trustees of the British Museum

The Nov. 21, 2013 University of Adelaide, news release, which originated the news item, explains why the Lycurgus Cup is of such interest, and why the same cup can be green or red

The Lycurgus Cup, a 4th century cup held by the British Museum in London, is made of glass which changes colour from red to green depending on whether light is shining through the Cup or reflected off it. It gets this property from gold and silver nanoparticles embedded in the glass.

“The Lycurgus Cup is a beautiful artefact which, by accident, makes use of the exciting properties of nanoparticles for decorative effect,” says Associate Professor Ebendorff-Heidepriem. “We want to use the same principles to be able to use nanoparticles for all sorts of exciting advanced technologies.”

Nanoparticles need to be held in some kind of solution. “Glass is a frozen liquid,” says Associate Professor Ebendorff-Heidepriem. “By embedding the nanoparticles in the glass, they are fixed in a matrix which we can exploit.”

Associate Professor Ebendorff-Heidepriem is leading a three-year Australian Research Council Discovery Project to investigate how best to embed nanoparticles; looking at the solubility of different types of nanoparticles in glass and how this changes with temperature and glass type, and how the nanoparticles are controlled and modified.

Practical applications, according to the news release, include,

“Nanoparticles and nanocrystals are the focus of research around the world because of their unique properties that have the potential to bring great advances in a wide range of medical, optical and electronic fields,” says Associate Professor Heike Ebendorff-Heidepriem, Senior Research Fellow in the University’s School of Chemistry and Physics. “A process for successfully incorporating nanoparticles into glass, will open the way for applications like ultra low-energy light sources, more efficient solar cells or advanced sensors that can see inside the living human brain.”

“We will be able to more readily harness these nanoscale properties in practical devices. This gives us a tangible material with nanoparticle properties that we can shape into useful forms for real-world applications. And the unique properties are actually enhanced by embedding in glass.”

A strange state of light

Apparently combining a hologram with subwavelength structures at a scale of just tens of nanometers can lead to ‘strange’ light. From the Aug. 20, 2013 news item on Nanowerk,

Applied physicists at the Harvard School of Engineering and Applied Sciences (SEAS) have demonstrated that they can change the intensity, phase, and polarization of light rays using a hologram-like design decorated with nanoscale structures.

As a proof of principle, the researchers have used it to create an unusual state of light called a radially polarized beam, which—because it can be focused very tightly—is important for applications like high-resolution lithography and for trapping and manipulating tiny particles like viruses.

The Aug. 20, 2013 Harvard University news release by Manny Marone, which originated the news item, further describes the device and the effect (Note: A link has been removed),

This is the first time a single, simple device has been designed to control these three major properties of light at once. (Phase describes how two waves interfere to either strengthen or cancel each other, depending on how their crests and troughs overlap; polarization describes the direction of light vibrations; and the intensity is the brightness.)

“Our lab works on using nanotechnology to play with light,” says Patrice Genevet, a research associate at Harvard SEAS and co-lead author of a paper published this month in Nano Letters. “In this research, we’ve used holography in a novel way, incorporating cutting-edge nanotechnology in the form of subwavelength structures at a scale of just tens of nanometers.” One nanometer equals one billionth of a meter.

Using these novel nanostructured holograms, the Harvard researchers have converted conventional, circularly polarized laser light into radially polarized beams at wavelengths spanning the technologically important visible and near-infrared light spectrum.

“When light is radially polarized, its electromagnetic vibrations oscillate inward and outward from the center of the beam like the spokes of a wheel,” explains Capasso [Federico Capasso, professor of applied physics]. “This unusual beam manifests itself as a very intense ring of light with a dark spot in the center.”

“It is noteworthy,” Capasso points out, “that the same nanostructured holographic plate can be used to create radially polarized light at so many different wavelengths. Radially polarized light can be focused much more tightly than conventionally polarized light, thus enabling many potential applications in microscopy and nanoparticle manipulation.”

The new device resembles a normal hologram grating with an additional, nanostructured pattern carved into it. Visible light, which has a wavelength in the hundreds of nanometers, interacts differently with apertures textured on the ‘nano’ scale than with those on the scale of micrometers or larger. By exploiting these behaviors, the modular interface can bend incoming light to adjust its intensity, phase, and polarization.

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

Nanostructured Holograms for Broadband Manipulation of Vector Beams by Jiao Lin, Patrice Genevet, Mikhail A. Kats, Nicholas Antoniou, and Federico Capasso. Nano Lett., Article ASAP DOI: 10.1021/nl402039y Publication Date (Web): August 5, 2013
Copyright © 2013 American Chemical Society

This article is behind a paywall.

I last wrote about Federico Carpasso’s work in an Oct. 16, 2013 posting, Harvard researchers look deeply into oily puddles as they rethink thin films and optical loss.

Bringing home the chilling effects of outer space

They’ve invented a new type of cooling structure at Stanford University (California) which reflects sunlight back into outer space. From the Apr. 16, 2013 news item on Azonano,

A team of researchers at Stanford has designed an entirely new form of cooling structure that cools even when the sun is shining. Such a structure could vastly improve the daylight cooling of buildings, cars and other structures by reflecting sunlight back into the chilly vacuum of space.

The Apr. 15, 2013 Stanford Report by Andrew Myers, which originated the news item, describes the problem the engineers were solving,

The trick, from an engineering standpoint, is twofold. First, the reflector has to reflect as much of the sunlight as possible. Poor reflectors absorb too much sunlight, heating up in the process and defeating the goal of cooling.

The second challenge is that the structure must efficiently radiate heat (from a building, for example) back into space. Thus, the structure must emit thermal radiation very efficiently within a specific wavelength range in which the atmosphere is nearly transparent. Outside this range, the thermal radiation interacts with Earth’s atmosphere. Most people are familiar with this phenomenon. It’s better known as the greenhouse effect – the cause of global climate change.

Here’s the approach they used,

Radiative cooling at nighttime has been studied extensively as a mitigation strategy for climate change, yet peak demand for cooling occurs in the daytime.

“No one had yet been able to surmount the challenges of daytime radiative cooling –of cooling when the sun is shining,” said Eden Rephaeli, a doctoral candidate in Fan’s [Shanhui Fan, a professor of electrical engineering and the paper's senior author] lab and a co-first-author of the paper. “It’s a big hurdle.”

The Stanford team has succeeded where others have come up short by turning to nanostructured photonic materials. These materials can be engineered to enhance or suppress light reflection in certain wavelengths.

“We’ve taken a very different approach compared to previous efforts in this field,” said Aaswath Raman, a doctoral candidate in Fan’s lab and a co-first-author of the paper. “We combine the thermal emitter and solar reflector into one device, making it both higher performance and much more robust and practically relevant. In particular, we’re very excited because this design makes viable both industrial-scale and off-grid applications.”

Using engineered nanophotonic materials, the team was able to strongly suppress how much heat-inducing sunlight the panel absorbs, while it radiates heat very efficiently in the key frequency range necessary to escape Earth’s atmosphere. The material is made of quartz and silicon carbide, both very weak absorbers of sunlight.

This new approach offers both economic and social benefits,

The new device is capable of achieving a net cooling power in excess of 100 watts per square meter. By comparison, today’s standard 10-percent-efficient solar panels generate about the same amount of power. That means Fan’s radiative cooling panels could theoretically be substituted on rooftops where existing solar panels feed electricity to air conditioning systems needed to cool the building.

To put it a different way, a typical one-story, single-family house with just 10 percent of its roof covered by radiative cooling panels could offset 35 percent its entire air conditioning needs during the hottest hours of the summer.

Radiative cooling has another profound advantage over other cooling equipment, such as air conditioners. It is a passive technology. It requires no energy. It has no moving parts. It is easy to maintain. You put it on the roof or the sides of buildings and it starts working immediately.

Beyond the commercial implications, Fan and his collaborators foresee a broad potential social impact. Much of the human population on Earth lives in sun-drenched regions huddled around the equator. Electrical demand to drive air conditioners is skyrocketing in these places, presenting an economic and environmental challenge. These areas tend to be poor and the power necessary to drive cooling usually means fossil-fuel power plants that compound the greenhouse gas problem.

“In addition to these regions, we can foresee applications for radiative cooling in off-the-grid areas of the developing world where air conditioning is not even possible at this time. There are large numbers of people who could benefit from such systems,” Fan said.

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

Ultrabroadband Photonic Structures To Achieve High-Performance Daytime Radiative Cooling by Eden Rephaeli, Aaswath Raman, and Shanhui Fan.  Nano Lett. [American Chemical Society Nano Letters], 2013, 13 (4), pp 1457–1461
DOI: 10.1021/nl4004283 Publication Date (Web): March 5, 2013
Copyright © 2013 American Chemical Society

The article is behind a paywall.

For anyone who might be interested in what constitutes hot temperatures, here’s a sampling from the Wikipedia List of weather records (Note: I have removed links and included only countries which experienced temperatures of 43.9 °C or 111 °F or more; I made one exception: Antarctica),




North America / On Earth

56.7 °C (134 °F) Furnace Creek Ranch (formerly Greenland Ranch), in Death Valley, California, United States 1913-07-10


45.0 °C (113 °F) Midale, Yellow Grass, Saskatchewan 1937-07-05


52 °C (125.6 °F) San Luis Rio Colorado, Sonora


55.0 °C (131 °F) Kebili, Tunisia 1931-07-07


50.6 °C (123.1 °F) In Salah, Tamanrasset Province 2002-07-12


44.5 °C (112 °F) Kandi  ?

Burkina Faso

47.2 °C (117 °F) Dori  ?


47.7 °C (117.9 °F) Kousseri  ?

Central African Republic

45 °C (113 °F) Birao  ?


47.6 °C (117.7 °F) Faya-Largeau 2010-06-22


49.5 °C (121 °F) Tadjourah  ?


50.3 °C (122.6 °F) Kharga  ?


48 °C (118.4 °F) Massawa  ?


48.9 °C (120 °F) Dallol  ?

The Gambia

45.5 °C (114 °F) Basse Santa Su 2008-?-?


43.9 °C (111 °F) Navrongo  ?


50.2 °C (122.4 °F) Zuara 1995-06


45 °C (113 °F) Ngabu, Chikwana  ?


48.2 °C (118 °F) Gao  ?


50.0 °C (122 °F) Akujit  ?


49.6 °C (121.3 °F) Marrakech 2012-07-17


47.3 °C (117.2 °F) Chibuto 2009-02-03


47.8 °C (118 °F) Noordoewer 2009-02-06


48.2 °C (118.8 °F) Bilma 2010-06-23


46.4 °C (115.5 °F) Yola 2010-04-03


47.8 °C (118 °F) Berbera  ?

South Africa

50.0 °C (122 °F) Dunbrody, Eastern Cape 1918


49.7 °C (121.5 °F) Dongola 2010-06-25


46.1 °C (115 °F) Sidvokodvo  ?


45.6 °C (114 °F) Beitbridge,  ?


53.6 °C (128.5 °F) Sulaibya, Kuwait 2012-07-31


45.1 °C (113.2 °F) Rajshahi 1972-04-30


49.7 °C (118 °F) Ading Lake, Turpan, Xinjiang, China 2008-08-03


50 °C (122 °F) Sri, Ganganagar, Rajasthan Dholpur, Rajasthan  ?


52.0 °C (125.7 °F) Basra, Ali Air Base, Nasiriyah 2010-06-14


53 °C (127.4 °F) Tirat Zvi, Israel 1942-06-21


47.0 °C (116.6 °F) Myinmu 2010-05-12


53.5 °C (128.3 °F) Mohenjo-daro, Sindh 2010-05-26


50.4 °C (122.7 °F) Doha 2010-07-14

Saudi Arabia

52.0 °C (125.6 °F) Jeddah 2010-06-22


44.5 °C (112.1 °F) Uttaradit 1960-04-27


48.8 °C (119.8 °F) Mardin 1993-08-14


50.7 °C (123.3 °F) Oodnadatta, South Australia, Australia 1960-01-02

South America

49.1 °C (120.4 °F) Villa de María, Argentina 1920-01-02


45 °C (113 °F) Pratts Gill, Boquerón Department 2009-11-14


44 °C (111.2 °F) Paysandú, Paysandú Department 1943-01-20

Central America and Caribbean Islands

45 °C (113 °F) Estanzuela, Zacapa Guatemala  ?


48.0 °C or 48.5 °C (118.4 °F or 119.3 °F) Athens, Greece or Catenuova, Italy (Catenanuova’s record is disputed) 1977-07-10 or 1999-08-10;

Bosnia and Herzegovina

46.2 °C (115.16 °F) Mosta (Herzegovina, Federation of Bosnia and Herzegovina) 1900-07-31


46.6 °C (115.9 °F) Letkoniko, Cyprus 2010-08-01


47 °C or 48.5 °C (116.6 or 119.3 °F) Foggia, Apulia or Catenuuova, Sicily (Catenanuova’s record is disputed) 2007-06-25 and 1999-08-10


45.7 °C(114.26 °F) Demir Kapija, Demir Kapija Municipality 2007-07-24


47.4 °C (117.3 °F) Amarelja, Beja 2003-08-01


44.9 °C (112.8 °F) Smederevska Palanka, Podunavlie Distrrict, 2007-07-24


47.2 °C (116.9 °F) Murcia 1994-07-04


14.6 °C (59 °F) Vanda Station, Scott Coast 1974-01-05

It seems a disproportionate number of these hot temperatures have been recorded since 2000, eh?

Structure of color

AGELESS BRILLIANCE: Although the pigment-derived leaf color of this decades-old specimen of the African perennial Pollia condensata has faded, the fruit still maintains its intense metallic-blue iridescence.COURTESY OF P.J. RUDALL [downloaded from]

AGELESS BRILLIANCE: Although the pigment-derived leaf color of this decades-old specimen of the African perennial Pollia condensata has faded, the fruit still maintains its intense metallic-blue iridescence.COURTESY OF P.J. RUDALL [downloaded from]

Hard to believe those berries were collected more than four decades ago, according to Cristina Luiggi in her Feb. 1, 2013 article, Color from Structure, for The Scientist magazine. Her focus is on biological nanostructures and it is a fascinating article which I urge you to read in its entirety if you have the time and this kind of thing interests you. As you can see, the pictures are great.

Here are a few excerpts from the piece,

Colors may be evolution’s most beautiful accident. Spontaneous mutations that perturbed the arrangement of structural components, such as cellulose, collagen, chitin, and keratin, inadvertently created nanoscale landscapes that catch light in the most vibrantly diverse ways—producing iridescent greens, fiery reds, brilliant blues, opalescent whites, glossy silvers, and ebony blacks.

Structural colors, in contrast to those produced by pigments or dyes, arise from the physical interaction of light with biological nanostructures. These color-creating structures likely developed as an important phenotype during the Cambrian explosion more than 500 million years ago, when organisms developed the first eyes and the ability to detect light, color, shade, and contrast. “As soon as you had visual predators, there were organisms that were either trying to distract, avoid, or communicate with those predators using structural coloration,” says Yale University evolutionary ornithologist Richard Prum.

Ever since, structural coloration has evolved multiple times across the tree of life, as a wide range of organisms developed ways to fine-tune the geometry of some of the most abundant (and often colorless) biomaterials on Earth, engineering grooves, pockets, and films that scatter light waves and cause them to interfere with each other in ways we humans happen to find aesthetically pleasing.

Here’s why color derived from structure doesn’t fade, from Luiggi’s article,

Pigments and dyes are molecules that produce colors by the selective absorption and reflection of specific wavelengths of electromagnetic radiation. Structural colors, on the other hand, rely exclusively on the shape of the material and not its chemical properties. While pigments and dyes degrade and their colors fade over time, some types of structural coloration, which rely on the same materials that make up tree bark, insect exoskeletons, and claws or nails, can persist hundreds, thousands, and even millions of years after the death of the organism.

Structural color can be found in a lot of plant life,

Although there are only a handful of known examples of structural colors in fruits, there are plenty to be found in the leaves and petals of plants. Within every family of flowering plants, there is at least one species that displays structural colors.

“The presence of structural colors, especially in flowers, is likely used by pollinators to spot the position of the flower and to recognize it better,” Vignolini [Silvia Vignolini, a physics postdoc at the University of Cambridge] explains. But in some plants, the evolutionary purpose of structural coloration is harder to pin down. The leaves of the low-lying tropical spikemoss Selaginella willdenowii, for example, produce blue-green iridescence when young and growing in the shade, and tend to lose the structural coloration with age and when exposed to high levels of light. The iridescence is achieved by cells in the leaves’ upper epidermis, which contain a few layers of cellulose microfibrils packed with different amounts of water. This ultrastructure is often absent in the leaves of the same species growing in direct sunlight. Researchers hypothesize that the spikemoss turns off its iridescence by changing the water content of the leaves’ cell walls, says Heather Whitney, a research fellow at the University of Bristol who studies iridescence in plants.

This capability is not limited to plants. Insects (jewel beetles and the morpho butterfly are often cited) and fish also have evolved to include structural color as protective or attractive devices, from Luiggi’s article,

The brightest living tissues on the planet are found in fish. Under ideal conditions, for example, the silvery scales of the European sardine and the Atlantic herring can act like near-perfect mirrors—reflecting up to 90 percent of incoming light. It is an irony of nature that these shiniest of structures are not meant to be flaunted, but are intended as camouflage.

“When you’re out in the open water, if you drop down below 10 to 30 meters, in any direction you look, the intensity of light is the same,” explains Nicholas Roberts, a physicist at the University of Bristol who specializes in bio-optics. At that depth, a perfect reflector, or mirror, would seem invisible, because light is equally reflected from all sides and angles.

It will be interesting to see if there’s any future discussion of the giant squid in the context of structural color since, according to very recent research (as per my Feb. 1, 2013 posting), it appears to be covered in gold leaf when observed in its habitat.

Luiggi’s article starts with an ornithologist and circles back in a discussion about the difficulty of creating nanostructures, soft matter condensed physics, and birds,

To create structural colors, organisms must master architecture at the nanoscale—the size of visible-light wavelengths. “But it turns out that biology doesn’t do a good job of creating nanostructures,” Prum says.

Instead, organisms create the initial conditions that allow those nanostructures to grow using self-organizing physical processes. Thus, organisms exploit what’s known as soft condensed matter physics, or “the physics of squishy stuff,” as Prum likes to call it. This relatively new field of physics deals with materials that are right at the boundaries of hard solids, liquids, and gases.

“There’ve been huge advances in this field in the last 30 years which have created rich theories of how structure can arise at the nanoscale,” Prum says. “It has been very applicable to the understanding of how structural colors grow.”

Soft condensed matter physics has been particularly useful in understanding the production of the amorphous nanostructures that imbue the feathers of certain bird species with intensely vibrant hues. The blue color of the male Eastern bluebird (Sialia sialis), for example, is produced by the selective scattering of blue light from a complex nanostructure of b-keratin channels and air pockets in the hairlike branches called feather barbs that give the quill its lift. The size of the air pockets determines the wavelengths that are selectively amplified.

While there’s better understanding of the mechanisms involved in structural color, scientists are a long way from replicating the processes, from the article,

“The three-dimensional nature of the structures themselves is just so complex,” says Vukusic. [physicist Peter Vukusic, a professor of natural photonics at the University of Exeter, UK] “Were it to be a simple periodic system with a regular geometry, you could easily put that into a computer model and run simulations all day. But the problem is that they are never perfectly periodic.”

This article is open access so, as I noted earlier, all you need is the time. As of my Feb. 6, 2013 posting, there was some new research announced about scientists making observations about the structural color in peacock feathers and applying some of those ideas to develop better resolution in e-readers.

Peacocks and their structural colour inspire better resolution in e-readers

Thank goodness birds, insects, and other denizens of the natural world have not taken to filing patents otherwise we’d be having some serious problems in the courts as I have hinted in previous postings including this March 29, 2012 posting titled, Butterflies give and give … .

This time, it’s the peacock which is sharing its intellectual property as per this Feb. 5, 2013 news item on ScienceDaily,

Now, researchers at the University of Michigan have found a way to lock in so-called structural color, which is made with texture rather than chemicals. A paper on the work is published online in the current edition of the Nature journal Scientific Reports.

In a peacock’s mother-of-pearl tail, precisely arranged hairline grooves reflect light of certain wavelengths. That’s why the resulting colors appear different depending on the movement of the animal or the observer. Imitating this system—minus the rainbow effect—has been a leading approach to developing next-generation reflective displays.

The University of Michigan Feb. 5, 2013 news release, which originated the news item, provides information about potential applications and more details about the science,

The new U-M research could lead to advanced color e-books and electronic paper, as well as other color reflective screens that don’t need their own light to be readable. Reflective displays consume much less power than their backlit cousins in laptops, tablet computers, smartphones and TVs. The technology could also enable leaps in data storage and cryptography. Documents could be marked invisibly to prevent counterfeiting.

Led by Jay Guo, professor of electrical engineering and computer science, the researchers harnessed the ability of light to funnel into nanoscale metallic grooves and get trapped inside. With this approach, they found the reflected hues stay true regardless of the viewer’s angle.

“That’s the magic part of the work,” Guo said. “Light is funneled into the nanocavity, whose width is much, much smaller than the wavelength of the light. And that’s how we can achieve color with resolution beyond the diffraction limit. Also counterintuitive is that longer wavelength light gets trapped in narrower grooves.”

The diffraction limit was long thought to be the smallest point you could focus a beam of light to. Others have broken the limit as well, but the U-M team did so with a simpler technique that also produces stable and relatively easy-to-make color, Guo said.

“Each individual groove—much smaller than the light wavelength—is sufficient to do this function. In a sense, only the green light can fit into the nanogroove of a certain size,” Guo said.

The U-M team determined what size slit would catch what color light. Within the framework of the print industry standard cyan, magenta and yellow color model, the team found that at groove depths of 170 nanometers and spacing of 180 nanometers, a slit 40 nanometers wide can trap red light and reflect a cyan color. A slit 60 nanometers wide can trap green and make magenta. And one 90 nanometers wide traps blue and produces yellow. The visible spectrum spans from about 400 nanometers for violet to 700 nanometers for red.

“With this reflective color, you could view the display in sunlight. It’s very similar to color print,” Guo said.

Particularly interesting (for someone who worked in the graphic arts/printing industry as I did) are the base colours being used to create all the other colours,

To make color on white paper, (which is also a reflective surface), printers arrange pixels of cyan, magenta and yellow in such a way that they appear to our eyes as the colors of the spectrum. [emphasis mine] A display that utilized Guo’s approach would work in a similar way.

To demonstrate their device, the researchers etched nanoscale grooves in a plate of glass with the technique commonly used to make integrated circuits, or computer chips. Then they coated the grooved glass plate with a thin layer of silver. When light—which is a combination of electric and magnetic field components—hits the grooved surface, its electric component creates what’s called a polarization charge at the metal slit surface, boosting the local electric field near the slit. That electric field pulls a particular wavelength of light in.

The base colours in printing are CMYK (cyan, magenta, yellow, black). At least, that was the case when I worked in the graphic arts industry and quick search on the web suggests that standard still holds.(Have I missed a refinement?) In any event, here’s an image that demonstrates how this new colour scale can be used,

University of Michigan researchers created the color in these tiny Olympic rings using precisely-sized nanoscale slits in a glass plate coated with silver. Each ring is about 20 microns, smaller than the width of a human hair. They can produce different colors with different widths of the slits. Yellow is produced with slits that are each 90 nanometers wide. The technique takes advantage of a phenomenon called light funneling that can catch and trap particular wavelengths of light, and it could lead to reflective display screens with colors that stay true regardless of the viewer's angle. Image credit: Jay Guo, College of Engineering

University of Michigan researchers created the color in these tiny Olympic rings using precisely-sized nanoscale slits in a glass plate coated with silver. Each ring is about 20 microns, smaller than the width of a human hair. They can produce different colors with different widths of the slits. Yellow is produced with slits that are each 90 nanometers wide. The technique takes advantage of a phenomenon called light funneling that can catch and trap particular wavelengths of light, and it could lead to reflective display screens with colors that stay true regardless of the viewer’s angle. Image credit: Jay Guo, College of Engineering

You can find more about this work in the ScienceDaily news item, which includes a link to the abstract, or in the University of Michigan news release, which includes more images from the scientists.