激光非均匀性和内光路热效应对远场特性的影响

高功率高能激光在光束控制系统(或称为内光路)中的传输距离比长程大气传输要短得多，但高功率密度的激光束在通过内光路时的热效应对远场光束质量会有显著影响。采用自编的四维仿真程序，详细计算了沿x方向呈线性变化的环状高功率激光束通过内光路的传输。用像散参数、桶中功率(PIB)和峰值光强位置描述了远场光束质量。研究表明，内光路的热效应(热晕)使得光束的峰值光强和可聚焦能力下降，降低了远场的光束质量，初始光束的非均匀性会影响光束的可聚焦能力并引起像散。值得指出的是，热晕是一种非线性效应，会影响光强分布和引起远场峰值光强位置的移动，对此给出了物理诠释，并用数值计算证实了物理分析。

Influence of Laser Non-Uniformity and Thermal Effects in an Inner Optical System on the Far-Field Behavior

Although for a real high-power and high-energy laser the propagation distance of lasers in the beam control system (or called the inner optical system) is much shorter than that in the long-distance atmosphere, the thermal effect of a high-power-density laser beam passing through the inner optical system remarkably affects the far-field beam quality. By using a four-dimensional simulation code, detailed numerical calculations are performed for the high-power laser propagation in the inner optical system, where an annular profile with linear non-uniformity in the x direction is used to model the high-power laser. The astigmatic parameter, power in the bucket (PIB) and position of the peak intensity are chosen as the parameters for characterizing beam quality in the far-field. It is found that the thermal effect in the inner optical system reduces the peak intensity and beam focusability, thus degrades the far-field beam quality. In addition, the non-uniformity of the initial beam affects the focusability and gives rise to the astigmatism. It is worth noting that the thermal blooming is a nonlinear effect, which affects the intensity distribution and results in a shift of the position of peak intensity in the far-field. The physical interpretation is given and confirmed by numerical results.