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High-power lasers at 2 µm are required for optical countermeasure applications, but can also be used for processing of materials where the mid-infrared laser wavelength provides an advantage. These applications can benefit from power scaling the 2 µm output, with the requirement to maintain a compact footprint. In particular, a Tm-doped slab laser design can be very compact, as an alternative to high power Tm:fiber lasers at 1.9 µm. It can be used directly for modulated continuous-wave output or for pumping Ho-doped lasers and amplifiers that emit at 2.1 µm.
We have directly compared Tm:YLF and Tm:LLF slab crystals (1.5 mm x 11 mm x 20 mm), in an otherwise identical diode end-pumped laser configuration, to evaluate the power scaling to 150 W of these two related materials. We will present the analysis of the thermal lens behaviour of that could not be fully supressed for Tm:LLF in the slab architecture when pumped at 450 W of incident pump power from the high-brightness 793 nm laser diode stack (Lasertel T6 Diode). Further power scaling to the 300 W output power level of Tm:YLF in a dual-end-pumped slab laser configuration will be presented, in which parasitic internal lasing has been supressed through careful consideration of the slab geometry.
The improved Tm:YLF laser will be used to pump a Ho:YAG slab (1.5 mm x 10 mm x 55 mm) to amplify seed pulses from a nanosecond Q-switched oscillator. A spatially and temporally resolved model has been developed to determine the optimal pump configuration and crystal dimensions to amplify seed pulses from 7 W average power at 10 kHz repetition rate, to upwards of 150 W at 2.1 µm. The model is based on rate equations and determines the distribution of thermal load throughout the crystal, permitting accurate prediction of saturation- and thermal-induced aberrations in the amplifier.
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