Ld End-pumped Laser Three-level Thermal Effects Study

Diode-pumped all-solid-state lasers (DPSSL) has a lot of advantages, such as high optical-optical conversion efficiency and high stability, small volume and long life. It is widely used in national defence, photoelectron industry,communication, medical treatment and sanitation.Laser crystal is the core of diode-pumped all-solid-state lasers, which decide the output powers from continuous-wave end-pumped solid-state lasers. With the development of high power diode lasers, high power DPSSL has become one of the main objectives of current research and development activities within the laser community.Research of DPSSL has mainly concentrated on scaling of output power,while remaining of a high spatial beam quality. For this researchers have done a lot of fruitful efforts, and almost all of the efforts to address, directly or indirectly harmful to thermal problems, namely thermal effect. The thermal effects of the three-level laser crystals pumped by LD is numerically simulated and experimentally measured. The thermal focal length is obtained on the basis of solving the crystal temperature and temperature distribution inside the crystal. The experimental results are consistent with the theoretical results. The main content can be summarized as follows:1. First of all, overview of the development of solid-state lasers and blue lasers were reviewed. The development process of solid-state lasers and Trends were described. The advantages of solid-state lasers were explained and solid-state lasers applications were listed. Common laser crystals in science and technology and their respective characteristics were described. The blue laser used widely are also illustrated.2. There is serious thermal effects in experimental process of blue laser generated by LD pumping Nd:YAG SHG LBO. But the previous physical model does not take into account the difference of three-level and four-level during the calculation of heat effects, which result in the great difference between numerical simulation of the existing model and the actual conditions. We re-established modeland modified the heat transfer. We also numerically soluted the Poisson equation with matlab to get a more accurate temperature distribution inside the crystal, the internal temperature of crystal has improved greatly compared tohe numerical results before modifying the model. The therotical thermal focal length is obtained on this basis. The thermal focal length is also measured by experiment. Experimental results are consistent with the theoretical calculation.3. Thermal effect of quasi-three level by pulsed LD pumping crystal were studied. The Poisson Equation were numerically solved with matlab. The internal temperature distribution of the crystals was obtained when time changes. The results show that internal temperature reduces with the pulsed pump compared to continuous pumping and relieve thermal effects. The impact of the pulse interval, the pump radius and the crystal radius towards temperature change law was analysed and compared with matlab. Numerical results show that changes in pulse interval time does not have an impact on the temperature distribution inside the crystal when the pulse interval is too small compared with the thermal relaxation time. The temperature inside the crystal remains the same when the pulse interval time changes. When the pulse intervals can be compared to the thermal relaxation time, increasing the pulse interval can reduce the temperature inside the crystal. Results also show that the pump radius will affect the thermal effect inside the crystal, reducing the pumpping radius can increase the thermal effect. Crystal radius size also affects the temperature distribution inside the crystal, the smaller of thecrystal radius, the higher of the temperature, the more obvious of thermal effects.