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