Infrared semiconductor lasers for DIRCM applications

Abstract

We report on the development and characteristics of infrared semiconductor lasers as compact and robust light sources for Directed Infrared Countermeasures (DIRCM). The short-wavelength side of the 2-5 μm wavelength band of interest can be covered by GaSb-based optically pumped semiconductor disk lasers (OPSDLs), delivering a continuous-wave (cw) or temporally modulated multiple-Watt output with a high beam quality (M²<3). For the 3.7-5 μm wavelength range InP-based quantum cascade (QC) lasers are the best suited semiconductor laser source, delivering several hundreds of mW of average output power in a nearly diffraction limited output beam (M²<2). Further up-scaling of the output power can be achieved for OPSDLs by intra-cavity coupling of several semiconductor chips as gain elements in a multiple-disk cavity arrangement. For a 2.3 µm emitting dual-disk OPSDL, a doubling of the maximum roomtemperature output power compared to that of a comparable single-chip OPSDL has been demonstrated. For QC lasers power scaling by beam-quality-preserving beam combining has been demonstrated via polarization coupling of the output beams of two individual QC lasers, yielding a coupling efficiency of 82%.