Study On Slab Laser Amplifiers Thermal Effect Influence Of Transmission Characteristics

Slab laser amplifier has advantages of long lifetime, high conversion efficiency, small divergence angle, and simple structure. Due to all these advantages, the slab laser amplifier has attracted a lot of interests in many applications including military areas and health cares. However, in recent years, the thermal effect becomes serious problem that lowers the signal quality of the high power output, and limits the development for the device. Thus, the research on the slab’s thermal effect based on the slab’s transmission is highly expected in our letters.Using the static heat conduction equation and taking into account the finite difference approach, we have reasearch on the thermal effect for the slab amplifier which is end pumped by the high power laser diode array. Firstly, we numerical simulate the temperature distribution of the Nd:YAG slab crystal. Then the material thermal stress distribution and thermal strain distribution are further obatined. After that, the refractive index for crystal is finally derived in our letter. Based on these reaseches, we analyze the influence of thermal effect for the light beam transmiting in slab medium, and then find a way to improve the performance of the temperature distribution, reduce the thermal effect, and increase the output power of the laser.This thesis is structured as two parts. Part one is the research on the thermal effect of the slab laser amplifiers, and part two concentrates on the influence of the thermal effect for the light propagation in the laser amplifiers. Particularly, the calculation of the slab’s temperature distribution plays most important role. To slove this problem, we use the finite difference method to simulate the temperature field distribution at any pumps and cooling conditions. According to Hooke’s law, the thermal stress distribution is obtained by using the relationship between the stress and the strain. Based on this optical characteristics, the refractive index changes caused by the variation of the temperature and the stress can be finally derived.The dependence of the transmission characteristic for slab on the distribution of refractive index is investgared in this thesis. The transmission model for the slab laser amplifiers is established. The influence of thermal effect on the transmission of the super-gaussian beam is analyed. This performance could easily lead to the stress birefringence and the nonlinear effect for the signals. Utilizing the step Fourier algorithm, the space diffraction equation is then solved. Considering the diffractive modulation and nonlinear modulation, we could obtain the output signals from two polarization directions. Finally, the dependence for the signals on the slab transfer characteristic and the thermal effect is further discussed.