A Submicroscopic Tunable, Optical Amplifier

The new light-amplifying nanoparticle consists of a 190-nanometer diameter sphere of barium tin oxide surrounded by a 30-nanometer-thick shell of gold (Source: A. Manjavacas / Rice)

The new light-amplifying nanoparticle consists of a 190-nanometer diameter sphere of barium tin oxide surrounded by a 30-nanometer-thick shell of gold (Source: A. Manjavacas / Rice)

Rice University photonics researchers have unveiled a new nano­particle amplifier that can generate infrared light and boost the output of one light by capturing and converting energy from a second light. The innovation from Rice’s Laboratory for Nano­photonics LANP is a device functions much like a laser. But while lasers have a fixed output frequency, the output from Rice’s nanoscale optical para­metric amplifier (OPA) can be tuned over a range of frequencies that includes a portion of the infrared spectrum.

“Tunable infrared OPA light sources today cost around a $100,000 and take up a good bit of space on a tabletop or lab bench,” said study lead author Yu Zhang. “What we’ve demonstrated, in principle, is a single nano­particle that serves the same function and is about 400 nanometers in diameter.” Zhang said shrinking an infrared light source to such a small scale could open doors to new kinds of chemical sensing and molecular imaging that aren’t possible with today’s state-of-the-art nanoscale infrared spectros­copy.

Zhang said parametric amplification has been used for decades in micro­electronics. It involves two input signals, one weak and one strong, and two corres­ponding outputs. The outputs are also strong and weak, but the energy from the more powerful input is used to amplify the weak incoming signal and make it the more powerful output. The low-power output, idler, contains a residual fraction of the pump energy.

“Optical para­metric amplifiers operate with light rather than elec­tricity,” said LANP Director Naomi Halas. “In OPAs, a strong pump light dramatically amplifies a weak seed signal and generates an idler light at the same time. In our case, the pump and signal frequencies are visible, and the idler is infrared.” While the pump laser in Rice’s device has a fixed wavelength, both the signal and idler frequencies are tunable. “People have previously demonstrated nanoscale infrared lasers, but we believe this is the first tunable nano­scale infrared light source,” Halas said.

The breakthrough is the latest for Halas’ lab, the research arm of Rice’s Smalley-Curl Institute that specializes in the study of light-activated nanoparticles. For example, some metallic nano­particles convert light into plasmons, waves of electrons that flow like a fluid across a particle’s surface. In dozens of studies over the past two decades, LANP researchers have explored the basic physics of plasmonics and shown that plasmonic interactions can be harnessed for appli­cations as diverse as medical diagnostics, cancer treatment, solar-energy collection and optical computing.

One of LANP’s specialties is the design of multi­functional plasmonic nano­particles that interact with light in more than one way. Zhang said the nanoscale OPA project required LANP’s team to create a single particle that could simul­taneously resonate with three frequencies of light. “There are intrinsic ineffi­ciencies in the OPA process, but we were able to make up for these by designing a surface plasmon with triple resonances at the pump, signal and idler fre­quencies,” Zhang said. “The strategy allowed us to demonstrate tunable emission over a range of infrared frequencies. This is an important step for further development of the technology.” (Source: Rice)

Reference: Y. Zhang et al.: Toward Surface Plasmon-Enhanced Optical Parametric Amplification (SPOPA) with Engineered Nanoparticles: A Nanoscale Tunable Infrared Source, Nano Lett. 16 (5), 3373 (2016); DOI:10.1021/acs.nanolett.6b01095

Link: Laboratory for Nanophotonics LANP (N. Halas), Rice University, Houston, Texas, USA

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