Numerical modelling of Cr:YAG Q-switched Yb:YAG micro-lasers and comparison with experimental results

Abstract

Some applications like range finding, optical counter measures or engine ignition, require lasers capable of delivering high repetition rate bursts of nanosecond pulses with hundreds of microjoules to a few millijoules in terms of energy per pulse.We previously developed such a diode-pumped Yb:YAG micro-laser with an oscillator delivering 250 µJ to 300 µJ per pulse, with a 3 -5 ns pulse duration, with an intra-burst pulse repetition frequency that can be tuned continuously from 1 kHz to 20 kHz by increasing the pump power. This oscillator had been amplified to the mJ level by an additional laser module.But there is a large choice of possible dopant concentration and thickness for the Yb:YAG laser crystal, of low power transmittance value for the Cr:YAG passive Q-switching crystal and of pump power and burst duration, and we want to be sure the choice of design we make is the best one.In order to optimize this choice of design for the micro-laser, this paper, we developed a numerical model of laser amplification and passive Q-switch. After presenting the model, we describe how it compares with previous results from our own experimental results, in terms of energy per pulse, pulse duration and repetition frequency of the laser and how we managed to obtain good agreement with the experiments by optimizing the numerical modelling of the overlap between the laser and pump beams in the amplifying medium.Finally, future work to verify the reliability of the numerical model and to use it for optimization of the architecture of the passively Q-switched laser is presented.