First Nanoscale Tunable Infrared Source 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 has been demonstrated by photonics researchers at Rice University.

The creation of Rice’s Laboratory for Nanophotonics (LANP), the device functions similar to a laser. While lasers have a fixed output frequency, however, 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.

Study lead author Yu Zhang said:

“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. What we’ve demonstrated, in principle, is a single nanoparticle that serves the same function and is about 400 nanometers in diameter.”

That is around 15 times smaller than a red blood cell. 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.

light-amplifying nanoparticle
Rice University’s new light-amplifying nanoparticle consists of a 190-nanometer diameter sphere of barium tin oxide surrounded by a 30-nanometer-thick shell of gold. Credit: Alejandro Manjavacas /Rice University

LANP Director Naomi Halas, the lead scientist on the new study and the director of Rice’s Smalley-Curl Institute, said:

“Optical parametric amplifiers operate with light rather than electricity. 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.

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—an important potential step for further development of the technology.”

Study: Toward Surface Plasmon-Enhanced Optical Parametric Amplification (SPOPA) with Engineered Nanoparticles: A Nanoscale Tunable Infrared Source, Nano Letters (2016). DOI: 10.1021/acs.nanolett.6b01095

Top Image: Yu Zhang. Credit: Jeff Fitlow/Rice University