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  • Widely Tunable MIR QCL Eyed for Spectroscopy, Chemical Sensing
Jun 2016
EVANSTON, Ill., June 9, 2016 — A broadband-tunable IR laser has demonstrated the ability to capture the unique spectral fingerprints of gases. The monolithic laser technology is compact, and is expected to have applications in spectroscopy and chemical sensing.
Picture of the tunable laser system with GPIB transceiver and power supply. The main system measures 127 ×  203 × 184 mm. Courtesy of W. Zhou, et al./Scientific Reports.
The laser only has one moving part — a fan for cooling purposes — which Northwestern University professor Manijeh Razeghi cited as a major advantage over existing systems. Most such lasers require mechanical parts to achieve tuning. It operates in the 6.2- to 9.1-μm wavelength range with a single emitting aperture by integrating an 8-laser sampled grating distributed feedback laser array with an on-chip beam combiner, and its gain medium is based on a 5-core heterogeneous quantum cascade laser wafer.

Razeghi and her team integrated the laser into a system that contains all of the laser driver electronics and tuning software necessary for integration into a spectroscopy system. It produces a stable, single-aperture spot less than 3 mm in diameter that is suitable for standoff detection and is capable of linear or random access scanning with stabilization times of less than 1 ms per wavelength.

Initial results were published in Scientific Reports (doi: 10.1038/srep25213).

The laser system R&D is the culmination of more than 18 years of quantum cascade laser development work at Northwestern's Center for Quantum Devices, which Photonics Media has covered continuously. The work was supported by the Department of Homeland Security Science and Technology Directorate, National Science Foundation, Naval Air Systems Command, DARPA and NASA.

quantum cascade laser
A Quantum Cascade Laser (QCL) is a type of semiconductor laser that emits light in the mid- to far-infrared portion of the electromagnetic spectrum. Quantum cascade lasers offer many benefits: They are tunable across the mid-infrared spectrum from 5.5 to 11.0 µm (900 cm-1 to 1800 cm-1); provide a rapid response time; and provide spectral brightness that is significantly brighter than even a synchrotron source. Quantum cascade lasers comprise alternating layers of semiconductor...
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