Research On Thermal Effect Of High Power LD Side-pumped Nd:YAG Laser

High-power solid-state lasers play an important role in scientific research,industry,military and medical treatment.Thermal effects restrict the further improvement of laser output power and beam quality.Therefore,it is of great significance to study the thermal effects and take measures to improve the performance of lasers.This paper established a thermal analysis model for high-power laser diode(LD)side-pumped Nd:YAG lasers under uneven pump to discuss the thermal effects.This paper analyzed thermal mechanism of solid-state lasers and the mechanical structure of LD side-pumped solid-state laser,including the laws for the thermal conductivity and the surface heat-transfer coefficient of crystal under different temperatures.With considering thermal relaxation time,the thermal distribution was proved to reach a steady-condition for Nd:YAG lasers at high repetition rate and the temperature and thermal stress distribution could be solved with the heat conduction equation.Tracing the pump light could obtain the light intensity of the crystal boundary,using the finite element could build the thermal analysis model of LD side pumped Nd:YAG laser under non-uniform pumping conditions.Therefore,solving the absorption equation and two-dimensional heat equation could plot the absorption power distribution and the temperature changes on the crystal cross section.Finally,according to the temperature gradient and the heat balance equation,the thermal stress in the crystal was able to be solved.By using the thermal analysis model,the factors which influenced the thermal effects were investigated,such as repetition frequency,the divergence angle,the doping concentration and the diameter of the crystal and the distance from the centre of the crystal to the pump source.Based on the theoretical model,an optimized laser module was achieved.The theoretical simulation results were compared between the thermal analysis model developed by author and LASCAD.The fluorescence spatial distribution of the non-optimized and optimized laser module was measured.A birefringence experiment using He-Ne laser was designed and the influence of the thermal birefringence on the laser performance was researched in experiment and theory.