High-power diode lasers for the 1.9 to 2.2 µm wavelength range

GaSb based diode laser both as single emitters and as linear arrays, emitting between 1.9 and 2.2 µm, have a huge potential especially for materials processing, medical applications and as optical pump sources for solid state laser systems emitting in the 2-4 µm wavelength range. Determined by the absorption characteristics of thermoplastic materials at wavelength around 2 µm, the light emitted by the diode laser will be absorbed by the material itself and can thus be used for marking and welding without the addition of e.g. colour pigments. We will present results on different (AlGaIn)(AsSb) quantum-well diode laser single emitters and linear laser arrays, the latter consisting of 20 emitters on a 1 cm long bar, emitting at different wavelengths between 1.9 and 2.2 µm. To improve on the typically poor fast axis beam divergence of diode lasers emitting at these wavelengths, we abandoned the broadened waveguide concept and changed over to a new waveguide design which features a rather narrow waveguide core. This results in a remarkable reduction in fast axis beam divergence to 43° FWHM for the new waveguide design. Electro-optical and thermal behaviour and the wavelength tunability by current and temperature have been carefully investigated in detail. For single emitters cw output powers of 2 W have been demonstrated. For diode laser arrays mounted on actively cooled hat sinks, more than 20 W in continuous-wave mode have been achieved at a heat sink temperature of 20 °C resulting in wall-plug efficiencies of more than 26%.