光束控制系统热效应与球差对激光光束质量的影响

采用Strehl比、桶中功率、β参数和束宽描述远场光束质量，研究了光束控制系统热效应和球差对远场激光光束质量的影响.用四维仿真程序作了详细计算，给出了数值计算结果并进行了物理分析.研究表明，传输通道的热效应和正球差会使远场光强分布扩展，可聚焦能力下降，光束质量变差.有意义的是，当激光发射功率达到一定值时，合适选取负球差会在几何焦面得到比无球差时更高的峰值光强和更好的可聚焦能力.但在以前的工作中，由于焦移，类似的结论是在实际焦面上得出的.非线性热晕的存在是其物理原因，对此用数值计算例子作了说明. 关键词： 高功率激光 热效应 光束控制系统 球差

The influence of thermal effects in a beam control system and spherical aberration on the laser beam quality

With the strehl ratio, power in the bucket, β parameter and beam widths taken as the characteristic parameters of laser beam quality in the far field, the influence of thermal effects in a beam control system and spherical aberration on the laser beam quality in the far field is studied. Detailed calculations are performed using a four-dimensional simulation code, and numerical results are given and analyzed physically. It is shown that the thermal effects in the propagation channel and positive spherical aberration give rise to an expansion of intensity distributions and reduce the focus ability in the far field, and degrade the beam quality. It is interesting that a suitable choice of the negative spherical aberration would result in a higher peak intensity and a better focus abilty at the geometrical focal plane than that of the spherical-aberration-free case, as the emissive power reaches a certain value; whereas a similar result is achieved at the real focal plane due to the focal shift as in the previous work. The physical interpretation is that there exists the nonlinear thermal blooming, which is illustrated with numerical examples.