Simulations of the lasing properties of a thin-disk laser combining high-output powers with good beam quality

Abstract

A model to predict the optical efficiency and beam quality obtained from a diode pumped high-power thin disk laser is presented. The laser consists of a linear resonator with the quasi-three-level laser active material Yb:YAG placed as a thin disk on a cooling finger. The laser crystal is pumped by a near flat-top pump beam profile in a multiple pass configuration. Cw-output powers of 255 W at pump powers of 519 W have been achieved experimentally. Within the model the temperature distribution inside the crystal is calculated, taking into account the mutual dependence of temperature (and thus level population) and pump light absorption. The pump beam power distribution is modeled by Monte-Carlo-ray-tracing. The resonator is simulated by self-consistently circulating the power distribution within the resonator via transformations into a suitable mode system and back, using simple matrix multiplication. Thermal lensing due to thermo- optical and mechanical deformations is considered, using the results of finite-element-modeling. The resulting optical efficiency and beam quality have been calculated. The dependence on variables like temperature, dimensions of the pump beam source, number of pump beam passes and crystal thickness is discussed.