From a flat mirror, designer light

Researchers at Harvard create bizarre optical phenomena, defying the laws of reflection and refraction

2011-09-02

(Press-News.org) Cambridge, Mass. - September 1, 2011 - Exploiting a novel technique called phase discontinuity, researchers at the Harvard School of Engineering and Applied Sciences (SEAS) have induced light rays to behave in a way that defies the centuries-old laws of reflection and refraction.

The discovery, published this week in Science, has led to a reformulation of the mathematical laws that predict the path of a ray of light bouncing off a surface or traveling from one medium into another—for example, from air into glass.

"Using designer surfaces, we've created the effects of a fun-house mirror on a flat plane," says co-principal investigator Federico Capasso, Robert L. Wallace Professor of Applied Physics and Vinton Hayes Senior Research Fellow in Electrical Engineering at SEAS. "Our discovery carries optics into new territory and opens the door to exciting developments in photonics technology."

It has been recognized since ancient times that light travels at different speeds through different media. Reflection and refraction occur whenever light encounters a material at an angle, because one side of the beam is able to race ahead of the other. As a result, the wavefront changes direction.

The conventional laws, taught in physics classrooms worldwide, predict the angles of reflection and refraction based only on the incident (incoming) angle and the properties of the two media.

While studying the behavior of light impinging on surfaces patterned with metallic nanostructures, the researchers realized that the usual equations were insufficient to describe the bizarre phenomena observed in the lab.

The new generalized laws, derived and experimentally demonstrated at Harvard, take into account the Capasso group's discovery that the boundary between two media, if specially patterned, can itself behave like a third medium.

"Ordinarily, a surface like the surface of a pond is simply a geometric boundary between two media, air and water," explains lead author Nanfang Yu (Ph.D. '09), a research associate in Capasso's lab at SEAS. "But now, in this special case, the boundary becomes an active interface that can bend the light by itself."

The key component is an array of tiny gold antennas etched into the surface of the silicon used in Capasso's lab. The array is structured on a scale much thinner than the wavelength of the light hitting it. This means that, unlike in a conventional optical system, the engineered boundary between the air and the silicon imparts an abrupt phase shift (dubbed "phase discontinuity") to the crests of the light wave crossing it.

Each antenna in the array is a tiny resonator that can trap the light, holding its energy for a given amount of time before releasing it. A gradient of different types of nanoscale resonators across the surface of the silicon can effectively bend the light before it even begins to propagate through the new medium.

The resulting phenomenon breaks the old rules, creating beams of light that reflect and refract in arbitrary ways, depending on the surface pattern.

In order to generalize the textbook laws of reflection and refraction, the Harvard researchers added a new term to the equations, representing the gradient of phase shifts imparted at the boundary. Importantly, in the absence of a surface gradient, the new laws reduce to the well-known ones.

"By incorporating a gradient of phase discontinuities across the interface, the laws of reflection and refraction become designer laws, and a panoply of new phenomena appear," says Zeno Gaburro, a visiting scholar in Capasso's group who was co-principal investigator for this work. "The reflected beam can bounce backward instead of forward. You can create negative refraction. There is a new angle of total internal reflection."

Moreover, the frequency (color), amplitude (brightness), and polarization of the light can also be controlled, meaning that the output is in essence a designer beam.

The researchers have already succeeded at producing a vortex beam (a helical, corkscrew-shaped stream of light) from a flat surface. They also envision flat lenses that could focus an image without aberrations.

INFORMATION:

Yu, Capasso, and Gaburro's co-authors included Patrice Genevet, Mikhail A. Kats, Francesco Aieta, and Jean-Philippe Tetienne.

The research was supported by the National Science Foundation (NSF), the NSF-funded Harvard Nanoscale Science and Engineering Center, the Center for Nanoscale Systems at Harvard (part of the NSF-funded National Nanotechnology Infrastructure Network), the European Communities Seventh Framework Programme, and the Harvard Faculty of Arts and Sciences' Science Division Research Computing Group.

[Attachments] See images for this press release:

ELSE PRESS RELEASES FROM THIS DATE:

Two genes that cause familial ALS shown to work together

2011-09-02

NEW YORK, NY, (September 1, 2011) – Although several genes have been linked to amyotrophic lateral sclerosis (ALS), it is still unknown how they cause this progressive neurodegenerative disease. In a new study, Columbia University Medical Center (CUMC) researchers have demonstrated that two ALS-associated genes work in tandem to support the long-term survival of motor neurons. The findings were published in the September 1 online edition of the Journal of Clinical Investigation. "Any therapy based on this discovery is probably a long way off. Nonetheless, it's an important ...

Cornell physicists capture microscopic origins of thinning and thickening fluids

2011-09-02

ITHACA, N.Y. – In things thick and thin: Cornell physicists explain how fluids – such as paint or paste - behave by observing how micron-sized suspended particles dance in real time. Using high-speed microscopy, the scientists unveil how these particles are responding to fluid flows from shear – a specific way of stirring. (Science, Sept. 2). Observations by Xiang Cheng, Cornell post-doctoral researcher in physics and Itai Cohen, Cornell associate professor of physics, are the first to link direct imaging of the particle motions with changes in liquid viscosity. Combining ...

UT MD Anderson scientists discover secret life of chromatin

2011-09-02

HOUSTON -- Chromatin - the intertwined histone proteins and DNA that make up chromosomes – constantly receives messages that pour in from a cell’s intricate signaling networks: Turn that gene on. Stifle that one. But chromatin also talks back, scientists at The University of Texas MD Anderson Cancer Center report today in the journal Cell, issuing orders affecting a protein that has nothing to do with chromatin's central role in gene transcription - the first step in protein formation. "Our findings indicate chromatin might have another life as a direct signaling molecule, ...

ATS publishes clinical practice guidelines on interpretation of FENO levels

2011-09-02

The American Thoracic Society has issued the first-ever guidelines on the use of fractional exhaled nitric oxide (FENO) that address when to use FENO and how to interpret FENO levels in different clinical settings. The guidelines, which appear in the September 1 American Journal of Respiratory and Critical Care Medicine, are graded based on the available evidence in the literature. "There are existing guidelines to measure FENO but none to interpret the results," noted Raed A. Dweik, MD, chair of the guideline writing committee and professor of medicine and director ...

New map shows where tastes are coded in the brain

2011-09-02

Each taste, from sweet to salty, is sensed by a unique set of neurons in the brains of mice, new research reveals. The findings demonstrate that neurons that respond to specific tastes are arranged discretely in what the scientists call a "gustotopic map." This is the first map that shows how taste is represented in the mammalian brain. There's no mistaking the sweetness of a ripe peach for the saltiness of a potato chip – in part due to highly specialized, selectively-tuned cells in the tongue that detect each unique taste. Now, Howard Hughes Medical Institute and NIH ...

Ben-Gurion U. researchers identify gene that leads to myopia (nearsightedness)

2011-09-02

BEER-SHEVA, ISRAEL, September 1, 2011— A Ben-Gurion University of the Negev research group led by Prof. Ohad Birk has identified a gene whose defect specifically causes myopia or nearsightedness. In an article appearing online in the American Journal of Human Genetics today, Birk and his team reveal that a mutation in LEPREL1 has been shown to cause myopia. "We are finally beginning to understand at a molecular level why nearsightedness occurs," Prof. Birk says. The discovery was a group effort at BGU's Morris Kahn Laboratory of Human Genetics at the National Institute ...

2 brain halves, 1 perception

2011-09-02

Our brain is divided into two hemispheres, which are linked through only a few connections. However, we do not seem to have a problem to create a coherent image of our environment – our perception is not "split" in two halves. For the seamless unity of our subjective experience, information from both hemispheres needs to be efficiently integrated. The corpus callosum, the largest fibre bundle connecting the left and right side of our brain, plays a major role in this process. Researchers from the Max Planck Institute for Brain Research in Frankfurt investigated whether ...

Faster progress through puberty linked to behavior problems

2011-09-02

Children who go through puberty at a faster rate are more likely to act out and to suffer from anxiety and depression, according to a study by researchers at Penn State, Duke University and the University of California, Davis. The results suggest that primary care providers, teachers and parents should look not only at the timing of puberty in relation to kids' behavior problems, but also at the tempo of puberty -- how fast or slow kids go through puberty. "Past work has examined the timing of puberty and shown the negative consequences of entering puberty at an early ...

Sex hormones impact career choices

2011-09-02

Teacher, pilot, nurse or engineer? Sex hormones strongly influence people's interests, which affect the kinds of occupations they choose, according to psychologists. "Our results provide strong support for hormonal influences on interest in occupations characterized by working with things versus people," said Adriene M. Beltz, graduate student in psychology, working with Sheri A. Berenbaum, professor of psychology and pediatrics, Penn State. Berenbaum and her team looked at people's interest in occupations that exhibit sex differences in the general population and ...

First long-term study of WTC workers shows widespread health problems 10 years after Sept. 11

2011-09-02

In the first long-term study of the health impacts of the World Trade Center (WTC) collapse on September 11, 2001, researchers at The Mount Sinai Medical Center in New York have found substantial and persistent mental and physical health problems among 9/11 first responders and recovery workers. The data are published this week in a special 9/11 issue of the medical journal Lancet. The Mount Sinai World Trade Center Clinical Center of Excellence and Data Center evaluated more than 27,000 police officers, construction workers, firefighters, and municipal workers over the ...

In small preliminary study, fearful pet dogs exhibited significantly different microbiomes and metabolic molecules to non-fearful dogs, suggesting the gut-brain axis might be involved in fear behavior

Examination of Large Language Model "red-teaming" defines it as a non-malicious team-effort activity to seek LLMs' limits and identifies 35 different techniques used to test them

Most microplastics in French bottled and tap water are smaller than 20 µm - fine enough to pass into blood and organs, but below the EU-recommended detection limit

From a flat mirror, designer light

ELSE PRESS RELEASES FROM THIS DATE:

LAST 30 PRESS RELEASES: