Northwestern researchers demonstrate 100-W-level mid-IR QC lasers

Dec. 2, 2009
Researchers at Northwestern University (Evanston, IL) have achieved a breakthrough in pulsed quantum cascade laser (QCL) peak output power, delivering 120 W from a single device at room temperature.

Researchers at Northwestern University (Evanston, IL) have achieved a breakthrough in pulsed quantum cascade laser (QCL) peak output power, delivering 120 W from a single device at room temperature. The figure is a peak-power value for a QCL emitting 200 ns pulses at a 0.2% duty cycle.1 The device emits at a 4.45 micron wavelength from a 400-micron-wide aperture.

The results are attractive for IR countermeasures (a technique to disorient incoming IR-guided missiles to protect commercial and military aircraft).

Unlike conventional interband semiconductor lasers (diode lasers), the QCL is an intersubband device. Because of this fundamental difference, a QCL shows unique properties that a conventional laser lacks. One of these properties is that the linewidth enhancement factor of a QCL is close to zero, compared to two to five for a conventional laser. This difference has serious implications in terms of power scaling with broad-area devices.

Resistant to filamentation
Led by Manijeh Razeghi, the Northwestern researchers found that the QCL is exceptionally resistant to filamentation, a phenomenon that limits the ridge width of conventional broad-area semiconductor lasers. In this work, Razeghi's team demonstrated that the ridge width of a broad-area QCL can be increased up to 400 microns without suffering from filamentation. The room-temperature peak output power of as high as 120 W is up from 34 W only a year ago.

The mode number of the output is proportional to the laser's ridge width; the farfield output has two lobes at +/-38 degrees.

This work is partially supported by the Defense Advanced Research Projects Agency's Efficient Mid-Infrared Laser (EMIL) program. Additional funding is provided by the Office of Naval Research.

REFERENCE

1. Y. Bai et al., Applied Physics Letters 95, 221104 (2009).

About the Author

John Wallace | Senior Technical Editor (1998-2022)

John Wallace was with Laser Focus World for nearly 25 years, retiring in late June 2022. He obtained a bachelor's degree in mechanical engineering and physics at Rutgers University and a master's in optical engineering at the University of Rochester. Before becoming an editor, John worked as an engineer at RCA, Exxon, Eastman Kodak, and GCA Corporation.

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