With the continuous improvement of laser technology, laser technology has been more and more applied in various fields. Picosecond ultrashort pulse, because of high peak power, in the field of laser ranging, laser nuclear fusion(SG), precision machining, laser radar, biomedical, optical spectroscopy, photoelectron technology, satellite laser blinding weapons have important applications.For example, in satellite laser ranging and star load laser radar applications in, in order to be more effective and more accurately measured over long range target, picosecond laser has higher frequency, with high single pulse energy and good beam quality. But because of the narrow pulse width of picosecond and amplification efficiency low, usually use regenerative amplification and multistage MOPA amplification, in high repetition rate picosecond multistage amplifier, gain medium thermal effect will lead to shorter laser beam quality is poor, the amplification efficiency loss, light damage and other problems. This thesis focuses on the analysis of thermal effect of the gain medium, put forward the improvement method and experimental verification.The first chapter of this paper introduces the application of narrow pulse picosecond lasers in various fields, then introduces the research status of system analysis in side pumped MOPA narrow pulse amplification and bulk crystal thermal MOPA system. Research content of this article.The second chapter mainly analyzes the mechanism of the thermal effect of laser crystal, to research on how to improve the thermal effect of laser crystal, to ensure the normal work, to provide theoretical support to improve the laser beam quality and stability.The third chapter by LASCAD software to simulate the thermal effect of laser crystal and of amplifier gain medium temperature field distribution and stress field distribution and pumping direction are the number of different of gain medium influence the calculated and discussed. Through the simulation of the thermal effect of Nd:YAG rod crystal, it provides the data support for the next chapter.In the fourth chapter, the SESAM mode locking cavity is set up, which provides a seed source for the subsequent amplification, and the Nd:YVO4 crystal is used to make the output of the seed light polarized light. Then the principle of regenerative amplification is introduced, and the thermal lens of the side pumped Nd:YAG module is analyzed, which provides the data support for the regeneration chamber. In the traveling wave amplification process, the influence of thermal effect on the beam quality is analyzed, and the solution is proposed, The single pulse energy is obtained8.8m J, beam quality M~2_X=1.583? M~2_Y=1.418, divergence angle DivX=1.7mrad? DivY=2.0mrad. |