Diode lasers emitting at longer wavelengths between 1500 nm and 2500 nm open a wide range of defence applications as compact and efficient light sources in the fields of infrared countermeasures (IRCM), light detection and ranging (LIDAR) at so-called eye-safe wavelengths, or pumping of solid-state and optically pumped semiconductor lasers emitting in the 2-4 μm regime. Whereas for wavelengths below 1850 nm, InGaAsP/InP is naturally predestined for highpower diode lasers, beyond 1900 nm the GaSb-based (AlGaIn)(AsSb) material system offers clear advantages compared to InP-based diode lasers in terms of output power and wall-plug efficiency. Beside high output power, most of the applications request high beam quality. This so-called brightness can be realized in a cost-efficient and compact way by the tapered resonator concept which has been successfully established already in the 1 μm wavelength regime. For three specific wavelengths (1.5μm, 1.9μm, 2.3μm), broad-area lasers with 100 μm stripe width as well as 1 mm long ridge-waveguide lasers have been processed. Based on these results, an optimized resonator geometry has been derived for tapered devices aiming 1 W in CW operation and 2W in pulsed mode. For narrow-linewidth operation, the tapered devices are provided with anti-reflection coatings of less than 0.01% on both facets and can be spectrally stabilized with an external grating. Beside the electro-optical characterization, beam quality has been characterized in terms of near field and far field distribution and M2.
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