An output power of 120 W has been delivered by a single mid-infrared quantum cascade laser operating at room temperature, a breakthrough seen as important for future defense applications. The results, which are nearly four times the output power from a single device recorded a year ago, were achieved by Northwestern University researchers and are seen as particularly attractive for infrared countermeasure, a way of misguiding incoming missiles to protect commercial and military aircrafts. Unlike conventional interband semiconductor lasers, such as those used in DVD players, the quantum cascade laser (QCL) is an intersubband device that requires only electrons to operate. 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. The research, led by Manijeh Razeghi, Walter P. Murphy Professor of Electrical Engineering and Computer Science at the McCormick School of Engineering and Applied Science, was published this week in the journal Applied Physics Letters.Razeghi and researchers at the Center for Quantum Devices at Northwestern found that the QCL is exceptionally resistant to filiamentation, a phenomenon that limits the ridge width of conventional broad-area semiconductor lasers. Razeghi's team demonstrated that the ridge width of a broad-area QCL can be increased up to 400 µm without suffering from filiamentation. As a result, room temperature peak output power as high as 120 W was obtained from a single device, which is up from 34 W only a year ago. This work is partially supported by DARPA's Efficient Mid-Infrared Laser (EMIL) program. Additional funding is provided by the Office of Naval Research. For more information, visit: www.northwestern.edu