Broadly tunable and multi-spectral mid-IR semiconductor lasers and applications

Abstract

This paper describes an application-centric development of broadly tunable and multi-spectral mid/long-wave IR semiconductor lasers. Examples of various external-cavity lasers capable of broad, continuous wavelength tuning with type-I and type-II quantum cascade lasers are discussed. Laser configurations studied include conventional Littman-Metcalf, Littrow, multi-segment and Bragg-grating-coupled surface-emitting. All were capable of single-mode continuous tuning with high side-mode-suppression ratio. The lasers were evaluated with spectroscopic applications, which include wavelength-modulation spectroscopic imaging and multi-wavelength decomposition of a gas mixture. The results showed that these lasers were capable of maintaining wavelength accuracy and stability over the entire tuning range. Multispectral imaging with discrete wavelengths over a wide spectral range was also studied. The results with a modest 4-wavelength system demonstrated the potential application for target discrimination, detection, and identification. These results suggest potential value for broadly tunable, wide-band M/LWIR laser technology.