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 (M<sup>2</sup><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 (M<sup>2</sup><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%.
We present a study of the spectral characteristics of Fabry-Perot quantum cascade lasers in pulsed mode operation applying a time resolution of 3 ns in combination with a high spectral resolution of 0.02 cm<sup>-1</sup>. With this technique the laser spectra were investigated applying pulse lengths ranging between 100 ns and 20 μs and duty cycles between 0.01% and 10%. Depending on the current density and operation temperature, the spectra exhibit complex line patterns, which indicate mode competition caused by gain saturation effects.
We present measurements of the linewidth enhancement factor of a distributed feedback quantum cascade laser (DFB-QCL) using the so-called self-mixing technique. The linewidth enhancement factor is investigated by analyzing optical feedback induced changes of the emission properties of the laser. We will demonstrate that our self-mixing setup works well with QCLs in the mid infrared wavelength regime, and that it is possible to use the obtained signal to extract the linewidth enhancement factor. We present a setup that records the self-mixing signal with the voltage signal across the laser device using the laser as a detector itself. In this contribution we will show the advantages of this measurement technique. First measurements of the linewidth enhancement factor yield values that rise from 0.24 to 2.6 with an increase of the injection current of the QCL. We will discuss the influence of the injection current on the linewidth enhancement factor.
We present pulsed operation of index-coupled distributed feedback quantum cascade lasers based on the GaInAs/AlInAs/InP materials system emitting at a wavelength around 5.4 μm. The emission is single mode in the entire investigated temperature range between 240K and 350K with a side mode suppression ratio larger than 27 dB. These devices are employed in a fast gas detection experiment for the quantitative detection of nitric oxide. With the present measurement system minimum noise equivalent concentrations between 16.7 ppbv and 23.3 ppbv are obtained, corresponding to minimum detectable optical densities between 4.7•10<sup>-5</sup> and 6.5•<sup>10-5</sup>.