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Plasmons Enable Tunable IR Light Source

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A nanoscale optical parametric amplifier (OPA) has been demonstrated to function as a tunable IR light source. The device functions much like a laser; but while lasers have a fixed output frequency, the output from the nanoscale OPA can be tuned over a range of frequencies, including a portion of the IR spectrum. The device boosts the output of one light by capturing and converting energy from a second light.

Rice University's light-amplifying nanoparticle consists of a 190-nm-diameter sphere of barium tin oxide surrounded by a 30-nm-thick shell of gold.

Rice University's light-amplifying nanoparticle consists of a 190-nm-diameter sphere of barium tin oxide surrounded by a 30-nm-thick shell of gold. Courtesy of Alejandro Manjavacas/Rice University.

Rice University researchers developed the single-nanoparticle OPA by generating a surface plasmon-enhanced difference frequency by integrating a nonlinear optical medium, BaTiO3, in nanocrystalline form within a plasmonic nanocavity.

Study lead author Yu Zhang.
Study lead author Yu Zhang. Courtesy of Jeff Fitlow/Rice University.

These nanoengineered composite structures provided large enhancements of the confined fields and efficient coupling of the wavelength-converted idler radiation to the far-field. The result was a nanocomplex that worked as a nanoscale tunable IR light source.

"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," said researcher Yu Zhang. "The strategy allowed us to demonstrate tunable emission over a range of IR frequencies — an important potential step for further development of the technology."

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Lead scientist Naomi Halas.
Lead scientist Naomi Halas. Courtesy of Tommy LaVergne/Rice University.

Parametric amplification has been used for decades in microelectronics.

"Optical parametric amplifiers operate with light rather than electricity," said research 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. The researchers believe it’s the first instance of a tunable nanoscale IR light source. Commercially available tunable IR OPA light sources cost around $100,000 and have a large footprint; the Rice device is about 400 nm in diameter. Zhang said that shrinking an infrared light source to such a small scale may open doors to new kinds of chemical sensing and molecular imaging that are not possible with today's nanoscale IR spectroscopy.

The research was published in Nano Letters (doi: 10.1021/acs.nanolett.6b01095).

Published: May 2016
Glossary
photonics
The technology of generating and harnessing light and other forms of radiant energy whose quantum unit is the photon. The science includes light emission, transmission, deflection, amplification and detection by optical components and instruments, lasers and other light sources, fiber optics, electro-optical instrumentation, related hardware and electronics, and sophisticated systems. The range of applications of photonics extends from energy generation to detection to communications and...
nanophotonics
Nanophotonics is a branch of science and technology that explores the behavior of light on the nanometer scale, typically at dimensions smaller than the wavelength of light. It involves the study and manipulation of light using nanoscale structures and materials, often at dimensions comparable to or smaller than the wavelength of the light being manipulated. Aspects and applications of nanophotonics include: Nanoscale optical components: Nanophotonics involves the design and fabrication of...
infrared
Infrared (IR) refers to the region of the electromagnetic spectrum with wavelengths longer than those of visible light, but shorter than those of microwaves. The infrared spectrum spans wavelengths roughly between 700 nanometers (nm) and 1 millimeter (mm). It is divided into three main subcategories: Near-infrared (NIR): Wavelengths from approximately 700 nm to 1.4 micrometers (µm). Near-infrared light is often used in telecommunications, as well as in various imaging and sensing...
nano
An SI prefix meaning one billionth (10-9). Nano can also be used to indicate the study of atoms, molecules and other structures and particles on the nanometer scale. Nano-optics (also referred to as nanophotonics), for example, is the study of how light and light-matter interactions behave on the nanometer scale. See nanophotonics.
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