Thermal Effects Analysis In High-power Diode Pumped Cs Vapor Lasers

Being a new class of laser device, diode pumped alkali vapor lasers (DAPLs) has obtained a rapid development in recent years. They have both the advantages of gas lasers and solid lasers, which possess some desirable features such as high quantum efficiency, good optical quality and narrow-line-width (several MHz). DPALs can output high power lasers in near infrared spectrum with higher beam quality, and have extensive potential applications in laser cooling, directional energy transmission, material processing, atmospheric propagation and so on. During the past decades, the research on this laser has been carried out worldwide with some excellent results. To date, a cesium-ethane DPAL has obtained the highest slope efficiency of 81% and a rubidium-methane-helium DPAL has produced the record continuous wave (CW) output power of 145 W.Although DPALs have high quantum efficiency, the thermal effect will also appear to influence the laser beam quality and conversion efficiency when pursuing higher laser power. The thermal lensing effect changes the laser mode, and results in the mismatching of pump light to cavity mode. Therefore, it is important to study the thermal lensing effect for improving the output performance of DPALs. On the basis of our previous works on the kinetics and the spatial temperature distributions of DPALs, assuming the pump light to be Gaussian beam and considering the nonlinear absorption of medium, the heat conduction model is established to describe the thermal effects of double-end-pumped alkali lasers. According to the experimental parameters of Cs laser, the radial temperature distribution under different pump powers are calculated by numerically solving the model. Correspondingly, a description of the OPD is given. The results indicate that the radial temperature gradient and the OPD are increasing with the pump power. Furthermore, we analysis the effects of operating parameters, including the pump power, the buffer gas pressure, the cell temperature, and the pump beam waist, to the thermal focal length. It is found that it’s efficient to reduce thermal effects and improve the characters of output beams by enlarging the pump beam waist, decreasing the cell temperature and the pressure of buffer gas properly.According to different pump ways, we clarify the mechanism to scale the DPALs system to high powers in an end pumped way and in a side pumped way respectively. It can be predicted that the power of DPAL can achieve KW, even MW by flowing the gain medium in a side pumped way in near future.