激光振荡器内光束质量的演变机理对获得高光束质量激光至关重要。综合考虑激光晶体的热效应和增益导引效应,建立了激光振荡器的理论模型,仿真计算并实验验证了激光振荡器内光束质量的演变。基于理论模型,研究了光束质量演变的机理。指出带负球差激光通过激光晶体时,其负球差可以被晶体正球差补偿,从而改善光束质量。这一机理对激光振荡器和放大器实现高光束质量激光输出具有重要意义。 The evolution of beam quality within a laser oscillator is crucial to achieving a high beam quality laser. The theoretical model of the laser oscillator is established considering the thermal effect of the laser crystal and the gain guiding effect. The evolution of the laser beam quality in the laser oscillator is simulated and verified by experiments. Based on the theoretical model, the mechanism of beam quality evolution is studied. It is pointed out that when the negative spherical aberration laser passes through the laser crystal, the negative spherical aberration can be compensated by the spherical aberration of the crystal, so as to improve the beam quality. This mechanism is of great importance for achieving high beam quality laser output for laser oscillators and amplifiers.