Scientists and engineers from around the world will gather in the heart of Silicon Valley next week to discuss some of the latest breakthroughs in lasers and optics and their applications to cutting-edge science, the development of new materials, and medicine.
Journalists are invited to Frontiers in Optics (FiO) 2011/Laser Science XXVII—the 95th annual meeting of the Optical Society (OSA), which is being held together with the annual meeting of the American Physical Society (APS) Division of Laser Science at the Fairmont San Jose Hotel in San Jose, Calif. Oct 16-20. Registration details are below.
Many of the presentations at the meeting focus on the most cutting-edge discoveries in applied optics and fundamental physics. Some highlights, described below, include:
1. Tagging Tumors with Gold: Scientists Use Gold Nanorods to Flag Brain Tumors
2. Erasing History? Temporal Cloaks Adjust Light's Throttle to Hide an Event in Time
3. Borrowing from Brightly-colored Birds: Physicists Develop Lasers Inspired by Nature
Additional meeting and research highlights, including research on transforming an iPhone into a high-quality medical imaging device, can be found online in the FiO Media Center.
1. Tagging Tumors with Gold: Scientists Use Gold Nanorods to Flag Brain Tumors
"It's not brain surgery" is a phrase often uttered to dismiss a job's difficulty, but when the task actually is removing a brain tumor, even the slightest mistake could have serious health consequences. To help surgeons in such high-pressure situations, researchers from Prof. Adam Wax's team at Duke University's Fitzpatrick Institute for Photonics and Biomedical Engineering Department have proposed a way to harness the unique optical properties of gold nanoparticles to clearly distinguish a brain tumor from the healthy, and vital, tissue that surrounds it. The team will present their research next week at OSA's Frontiers in Optics 2011 meeting.
Current techniques for outlining brain tumors vary, but all have limitations, such as the inability to perform real-time imaging without big, expensive equipment, or the toxicity and limited lifespan of certain labeling agents. Gold nanoparticles—which are so small that 500 of them end-to-end could fit across a human hair—might provide a better way to flag tumorous tissue, since they are non-toxic and relatively inexpensive to manufacture.
The Duke researchers synthesized gold, rod-shaped nanoparticles with varying length-to-width ratios. The different-sized particles displayed different optical properties, so by controlling the nanorods' growth the team could "tune" the particles to scatter a specific frequency of light. The researchers next joined the tuned particles to antibodies that bind to growth factor receptor proteins found in unusually high concentrations on the outside of cancer cells. When the antibodies latched on to cancer cells, the gold nanoparticles marked their presence.
The team tested the method by bathing slices of tumor-containing mouse brain in a solution of gold nanoparticles merged with antibodies. Shining the tuned frequency of light on the sample revealed bright points where the tumors lurked. The tunability of the gold nanoparticles is important, says team member Kevin Seekell, because it allows researchers to choose from a window of light frequencies that are not readily absorbed by biological tissue. It might also allow researchers to attach differently tuned nanoparticles to different antibodies, providing a way to diagnose different types of tumors based the specific surface proteins the cancer cells display. Future work by the team will also focus on developing a surgical probe that can image gold nanoparticles in a living brain, Seekell says.
FiO presentation FWL4, "Controlled Synthesis of Gold Nanorods and Application to Brain Tumor Delineation," by Kevin Seekell et al. is at 11:45 a.m. on Wednesday, Oct. 19.
2. Erasing History? Temporal cloaks adjust light's throttle to hide an event in time
Researchers from Cornell University in Ithaca, N.Y., have demonstrated for the first time that it's possible to cloak a singular event in time, creating what has been described as a "history editor." In a feat of Einstein-inspired physics, Moti Fridman and his colleagues sent a beam of light traveling down an optical fiber and through a pair of so-called "time lenses." Between these two lenses, the researchers were able to briefly create a small bubble, or gap, in the flow of light. During that fleetingly brief moment, lasting only the tiniest fraction of a second, the gap functioned like a temporal hole, concealing the fact that a brief burst of light ever occurred.
Their ingenious system, which is the first physical demonstration of a phenomenon originally described theoretically a year ago by Martin McCall and his colleagues at Imperial College London in the Journal of Optics, relies on the ability to use short intense pulses of light to alter the speed of light as it travels through optical materials, in this case an optical fiber. (In a vacuum, light maintains its predetermined speed limit of 180,000 miles per second.) As the beam passes through a split-time lens (a silicon device originally designed to speed up data transfer), it accelerates near the center and slows down along the edges, causing it to balloon out toward the edges, leaving a dead zone around which the light waves curve. A similar lens a little farther along the path produces the exact but opposite velocity adjustments, resetting the speeds and reproducing the original shape and appearance of the light rays.
To test the performance of their temporal cloak, the researchers, who will present their findings next week at Frontiers in Optics 2011, created pulses of light directly between the two lenses. The pulses repeated like clockwork at a rate of 41 kilohertz. When the cloak was off, the researchers were able to detect a steady beat. By switching on the temporal cloak, which was synchronized with the light pulses, all signs that these events ever took place were erased from the data stream.
Unlike spatial optical cloaking, which typically requires the use of metamaterials (specially created materials engineered to have specific optical properties), the temporal cloak designed by the researchers relies more on the fundamental properties of light and how it behaves under highly constrained space and time conditions. The area affected by the temporal cloak is a mere 6 millimeters long and can last only 20 trillionths of a second. The length of the cloaked area and the length of time it is able to function are tightly constrained—primarily by the extreme velocity of light. Cloaking for a longer duration would create turbulence in the system, essentially pulling back the curtain and hinting that an event had occurred. Also, to achieve any measurable macroscopic effects, an experiment of planetary and even interplanetary scales would be necessary.
FiO presentation FMI3, "Demonstration of Temporal Cloaking," by Moti Fridman et al. is at 4:45 p.m. on Monday, Oct. 17.
3. Borrowing from Brightly-colored Birds: Physicists Develop Lasers Inspired by Nature
Researchers at Yale University are studying how two types of nanoscale structures on the feathers of birds produce brilliant and distinctive colors. The researchers are hoping that by borrowing these nanoscale tricks from nature they will be able to produce new types of lasers—ones that can assemble themselves by natural processes.
Many of the colors displayed in nature are created by nanoscale structures that scatter light strongly at specific frequencies. In some cases, these structures create iridescence, where colors change with the angle of view—like the shifting rainbows on a soap bubble. In other cases, the hues produced by the structures are steady and unchanging. The mechanism by which angle-independent colors are produced stumped scientists for 100 years: at first glance, these steady hues appeared to have been produced by a random jumble of proteins. But when researchers zoomed in on small sections of the protein at a time, quasi-ordered patterns began to emerge. The scientists found that it is this short-range order that scatters light preferentially at specific frequencies to produce the distinctive hues of a bluebird's wings, for example.
Inspired by feathers, the Yale physicists created two lasers that use this short-range order to control light. One model is based on feathers with tiny spherical air cavities packed in a protein called beta-keratin. The laser based on this model consists of a semiconductor membrane full of tiny air holes that trap light at certain frequencies. Quantum dots embedded between the holes amplify the light and produce the coherent beam that is the hallmark of a laser. The researchers, who will present their work next week at Frontiers in Optics 2011, also built a network laser using a series of interconnecting nanochannels, based on their observations of feathers whose beta-keratin takes the form of interconnecting channels in "tortuous and twisting forms." The network laser produces its emission by blocking certain colors of light while allowing others to propagate. In both cases, researchers can manipulate the lasers' colors by changing the width of the nanochannels or the spacing between the nanoholes.
What makes these short-range-ordered, bio-inspired structures different from traditional lasers is that, in principle, they can self-assemble, through natural processes similar to the formation of gas bubbles in a liquid. This means that engineers would not have to worry about the nanofabrication of the large-scale structure of the materials they design, resulting in cheaper, faster, and easier production of lasers and light-emitting devices.
One potential application for this work includes more efficient solar cells that can trap photons before converting them into electrons. The technology could also yield long-lasting paint, which could find uses in processes such as cosmetics and textiles. "Chemical paint will always fade," says lead author Hui Cao. But a physical "paint" whose nanostructure determines its color will never change. Cao describes a 40-million-year-old beetle fossil that her lab examined recently, and which had color-producing nanostructures. "With my eyes I can still see the color," she said. "It really lasts for a very long time."
Presentation FWW1, "Bio-inspired photonic nanostructures and lasers," by Hui Cao is at 4 p.m. on Wednesday, Oct. 19.
Genes affecting worm behavior found to be relevant to neurological disease in humans