LD End-pumped Green Laser And Their Thermal Effects

Laser diode (LD) end-pumped All-solid-state green laser has been promising application in the industry, military, scientific research, entertainment, medical fields and etc., due to their advantages, such as the small size, reliable operation, high efficiency, output laser with high beam quality, long life and so on. It has important significance to research the thermal effects of laser crystals which have seriously affected the output power and beam quality of all solid-state lasers.In this paper, the temperature characteristics of laser crystals by CW LD end-pumped and quasi-CW LD end-pumped in All-solid-state green laser were studied. The contents mainly were summarized as:1. The related theories of LD pumped All-solid-state green laser, including LD pump mode, the characters of several common laser crystals and nonlinear crystals, phase-matching principle, resonator cavity theory containing thermal lens, and the theory that using quasi-CW pump can improve the efficiency of frequency doubling, were summarized.2. For the thermal effects researches of laser crystals in LD end-pumped CW green laser.①Based on the working characteristic of laser rod end-pumped by LD, a thermal model of laser rod with adiabatic end faces and a fixed boundary temperature was introduced. Taking into account the pump light has the characteristics of super-Gaussian distribution, Nd:YAG is a thermal conductive isotropic material, Nd:YV04 is a thermal conductive anisotropic material, the temperature and heat flow is consecutive at the interface of composite crystal rod, analytical temperature field expressions of Nd:YAG rod, Nd:YVO4 rod, YAG-Nd:YAG rod were obtained respectively, by solving their thermal conduction equation in boundary conditions using the methods of eigen-function and constant variation. Meanwhile, the influences on the temperature field of crystal rod were quantitatively analyzed.②Based on the working characteristic of disk crystal end-pumped by LD, a thermal model of disk with adiabatic pump-face, adiabatic side face and cooling back temperature was established. A general analytical temperature field expression of the Nd:YAG disk was obtained. Some factors, such as different heat power densities of pump beam, different disk sizes and different doping concentrations, which influenced the temperature distribution of Nd:YAG disk, were analyzed quantitatively.3. For the thermal effects researches of quasi-CW LD end-pumped Q-switched pulse green laser.The laser crystal end-pumped by quasi-CW LD exist the temperature change process with heating, cooling, then heating, then cooling etc. transient thermal models of Nd:YAG rod and Nd:YAG disk that are true of practical working characteristics were established. Analytical solutions of transient temperature field of Nd:YAG rod, Nd:YAG disk in the quasi-CW working state were obtained, by solving their thermal conduction equation with time variable t using the methods of eigen-function and constant variation. Meanwhile, their transient temperature characteristics in quasi-CW working state were analyzed using the analytical solutions.The analytical solutions obtained by the new method used in the paper for solving the heat conductive equation has the characteristics of smaller calculation amount in the specific investigation of temperature distribution of laser rod. The methods and results can also be used to analyze all laser crystals pumped LD, and will play theoretically a directional role in improving the performance of lasers.