New Midinfrared Laser Diodes Emit More Light Than Heat

quantum-cascade-laser

A self-contained prototype quantum cascade laser pointer developed at CQD.

Researchers from Northwestern University (Evanston, IL) have developed compact, midinfrared laser diodes that generate more light than heat--a breakthrough in quantum-cascade laser efficiency. According to Manijeh Razeghi, the Walter P. Murphy professor of electrical engineering and computer science at the McCormick School of Engineering and Applied Science, the lasers have many potential applications in the medical device area.After years of research and industrial development, modern laser diodes in the near-infrared (approximately 1-µm) wavelength range are now extremely efficient. However the midinfrared range (greater than 3 µm) is much more difficult to access and has required the development of new device architectures.A diode laser designed on the quantum mechanical level to produce light at the desired wavelength with high efficiency, the quantum-cascade laser is unlike traditional diode lasers because it is unipolar, requiring only electrons to operate. Significant effort has been invested trying to understand and optimize the electron transport, which would allow researchers to improve laser quality and efficiency.Despite the special nature of these devices, laser wafer production is performed using standard compound semiconductor growth equipment. By optimizing the material quality in these standard tools, researchers at the Center for Quantum Devices (CQD) at Northwestern, led by Razeghi, have made significant breakthroughs in quantum-cascade laser performance.Previous high-efficiency quantum-cascade lasers have been limited to efficiency values of less than 40%, even when cooled to cryogenic temperatures. In contrast, after removing design elements unnecessary for low-temperature operation, researchers at CQD have now demonstrated individual lasers emitting at wavelengths of 4.85 µm with efficiencies of 53% percent when cooled to 40 K."This breakthrough is significant because, for the very first time, we are able to create diodes that produce more light than heat," says Razeghi. "Passing the 50% mark in efficiency is a major milestone, and we continue to work to optimize the efficiency of these unique devices."Though efficiency is currently the primary goal, the large demonstrated efficiencies can also be exploited to enable power scaling of quantum-cascade laser emitters. Recent efforts in broad-area quantum-cascade laser development have demonstrated individual pulsed lasers with record output powers up to 120 W, up from 34 W only a year ago.To read more about quantum-cascade lasers in the pages of Medical Product Manufacturing News, see "Slimmed-Down Mid-Infrared-Laser Sensor Could Make Waves in Handheld Devices."