Thermal compensation mechanism of concave lens in Tm: YAG continuous laser

We introduce a novel thermal compensation method for the LD end-pumped Tm:YAG laser as employing a concave lens into the resonator for the first time. Through theoretical analysis, we discover that thermal focal length decreases along with the increase of input pump power. Hence, the higher input pump power is, the shorter focal length of concave lens is needed. In experiments, we change the following three aspects to study the compensation effect: a) the focal length of concave lens(f), b) the total length of resonator(L), c) the distance between the rear end-face of Tm:YAG crystal and concave lens(l2). Under the experimental conditions of f = -50 mm, L = 200 mm and l2 = 14 mm, the best compensation result is obtained. As the input pump power reaches 31.10 W, compared to the uncompensated condition, the output power with concave lens is increased by 10.50 %. Therefore, employing a concave lens into the resonator is a credible method for thermal compensation of 2 μm laser output, which is of great significance for promoting the development and application of solid-state lasers.