Can silver nanoparticles be the key to a more compact laser?

“In random media, multiple scattering and interference reduce the diffusion of light, and in case of extremely strong scattering, photon localization, or Anderson localization of light, is predicted like electrons in glasses,” Katsuhisa Tanaka, a scientist in Kyoto University, tells PhysOrg.com. He and his colleagues are interested in using so-called disordered material to create lasers that could increase our understanding of physics – as well as make the laser creation process simpler.

With Xiangeng Meng, Koji Fujita (also doing work at PRESTO in Saitama, Japan), Yanhua Zong and Shunsuke Murai at Kyoto University, Tanaka has been working on using transparent films embedded with nanoparticles of silver to study the feedback coherence from certain random lasers. Their work can be seen in Applied Physics Letters: “Random lasers with coherent feedback from highly transparent polymer films embedded with silver nanoparticles.”

“Random lasers are laser sources that arise from multiple scattering events in random systems so that the strength of light scattering is of large importance in determining the feedback type of laser oscillation, Tanaka explains. “We are interested in such lasers because their fabrication process is technically simple while high gain is involved. At present, researchers are focusing on random lasers based on dielectrics with high refractive index, while little attention has been paid to metal nanostructures-based amplifying random media.”

He continues: “Actually, metal nanostructures are rather potential materials in laser devices. The use of surface plasmon resonance of metal nanostructures is extremely attractive because they bring about surface enhanced Raman scattering, enhancement of spontaneous emission, and amplified spontaneous emission, and so on. What we have consisdered for a long time is whether laser actions with high gain could be achieved by combining metal nanostructures and laser working medium.”

Indeed, this led Tanaka and his peers to wonder if surface plasmon resonance can help random lasing. The answer, in their minds, is yes: “We found that the presence of silver nanoparticles results in the coherent output even though the scattering strength of the system is very weak. We believe that surface plasmon plays an important role in the laser operation.”

In order to make the demonstration work, the Kyoto team embedded silver nanoparticles on highly transparent polymer films. The process was made possible through the in situ method, in which heat is used to create the hybrid material, combining polymer with metal in a way that is useful in terms of lasing. “We have calculated the transport mean free path of our sample and found that it is far larger than the sample size. The light propagates in such systems nearly freely without resistance,” Tanaks says. “Then, the issue that puzzles us is this: What on earth induces laser oscillation?”

Tanaka points out that silver nanoparticles make a difference: “First, localized optical modes near silver nanoparticle surface provide high optical gain for lasing. Second, scattering properties can be flexibly controlled by the size and shape of nanoparticles, and significantly contribute to light transport in random systems compared to that in dielectric nanoparticles.”

In terms of application, Tanaka sees possibilities for fundamental physics knowledge, as well as practical uses for this set-up. “Since the phenomena of random laser are reported for systems having very different scattering strength from nearly transparent to highly-scattering media, it is possible that the laser mechanism -- or dominating laser mode -- is different depending on the scattering strength. Thus the primal importance is to clarify the mechanism, which is beneficial to the progress of the physics.”

As far as practical applications, he says that there is a strong possibility of a compact laser. Plus, Tanaka continues, “Since this type of lasers does not require rigorous alignment of reflectors to form cavity in contrast to the conventional Fabry-Perot type ones, the making process is much simpler.”

The team at Kyoto continues to work on this project. Tanaka and his coworkers say that more needs to be known with regard to how the distribution of the silver nanoparticles within the polymer affects the laser. Additionally, they feel that this work could lead to advances in lasers that are based on organic semiconductors.

Copyright 2007 PhysOrg.com.
All rights reserved. This material may not be published, broadcast, rewritten or redistributed in whole or part without the express written permission of PhysOrg.com.

Related stories:

Killer pulses help characterize special surfaces
Detecting deadly fumes in subways, toxic gases in chemical spills, and hidden explosives in baggage is becoming easier and more efficient with a measurement technique called surface-enhanced Raman scattering. To further improve the technique's sensitivity, scientists must design better scattering surfaces, and more effective ways of evaluating them.
Cloudy day won't rain on laser communications
Just as clouds block the sun, they interfere with laser communications systems, but Penn State researchers are using a combination of computational methods to find the silver lining and punch through the clouds.
ORNL nanoprobe creates world of new possibilities
A technology with proven environmental, forensics and medical applications has received a shot in the arm because of an invention by researchers at the Department of Energy's Oak Ridge National Laboratory.
ORNL's nanoprobe, which is based on a light scattering technique, can detect and analyze chemicals, explosives, drugs and more at a theoretical single-molecule level. This capability makes it far more selective and accurate than conventional competing technologies.
Scientists take the sharpest image ever made with light
(PhysOrg.com) -- A team of scientists from the Technische Universität Dresden (Germany) and the ESRF in Grenoble (France) has produced the image of an object at the highest resolution ever achieved with X-ray light. A 100-nanometre gold particle fixed on a substrate was reconstructed with 5 nanometre resolution. Contrary to other techniques, X-ray imaging works also in real-life environments like chemical processing or in the presence of high magnetic fields. The team reports its findings in the newest issue of Phys. Rev. Lett. dated 5 September 2008 (published online 29 August 2008).
Physicists Transmit Light through Opaque Materials
No matter how thick an opaque "scattering material" is, physicists have shown how to weave light through tiny open channels in the material, so that the light passes through on the other side.
Forward step in forecasting global warming
Arizona State University researchers have made a breakthrough in understanding the effect on climate change of a key component of urban pollution. The discovery could lead to more accurate forecasting of possible global-warming activity, say Peter Crozier and James Anderson.
Skipping Atomic-scale Stones to Study Some Chemistry Basics
Thought experiment: a carbon dioxide molecule—think of a cheerleader’s baton—comes slanting in at high speed over a dense liquid, strikes the surface and ricochets. How does it tumble? Fast or slow? Forward, backward or sideways? These are not idle questions because simple events like the tumbling molecule go to the heart of the chemistry and physics of gas-liquid interactions. These cover a broad swath of important chemical processes—including breathing—for which details of the encounter are just coming into view.
New technology may help Olympic sailing
A team of researchers at the Ocean University of China has developed and tested a mobile lidar (light detection and ranging) station that can accurately measure wind speed and direction over large areas in real time -- an application useful for aviation safety, weather forecasting and sports.

News discussion:

Physics news