New Terahertz System Simpler, Clearer

Biosensing, space research and the ability to see through opaque surfaces without x-rays are all enabled by terahertz radiation. However, such systems have long been elusive.

A team from Northwestern University has produced terahertz radiation in a simplified system, making it easier to harness the power of such waves. Existing terahertz systems are expensive and large, with numerous components that require complex technologies, such as vacuum electronics, external pump lasers and cryogenic cooling. Often, they are too difficult to generate and manipulate.

The new continuous terahertz radiation scheme is compact and, in the study, demonstrated six times more efficiency than previous systems, the researchers said. It works well at room temperature and can be used effectively with high-power quantum cascade lasers (QCLs).

Graph showing THz peak power as a function of current and emitting spectrum at 10 amps. Courtesy of Applied Physics Letters.

“Continuous terahertz operation at room temperature is of utter importance to the wide application and commercialization of our lasers,” said Manijeh Razeghi, lead researcher and director of the Center for Quantum Devices in the McCormick School of Engineering and Applied Science at Northwestern.

The team generated terahertz radiation through nonlinear frequency mixing of two mid-infrared wavelengths at 8.8 µm and 9.8 µm from a single QCL chip. This allowed continuous terahertz emission with 3 µW realized in a compact, monolithic nonlinear QCL device.

The researchers achieved this by improving the thermal conductance with epilayer-down bonding and a buried ridge waveguide. The optical loss was also decreased with a buried composite grating for stable, single-mode operation.

Razeghi said that the new system could make terahertz radiation more accessible for experiments.

The work was funded by the National Science Foundation, the Department of Homeland Security, Naval Air Systems Command and NASA. The research was published in Applied Physics Letters (doi: 10.1063/1.4881182). LINK: http://scitation.aip.org/content/aip/journal/apl/104/22/10.1063/1.4881182

For more information, visit www.northwestern.edu.