寄生反射对高功率激光小尺度自聚焦的影响

Effect of Reflection on High Power Small-Scale Self-Focusing

寄生反射是影响高功率激光近场质量的重要因素之一。以Bespalov-Talanov理论为基础,重点分析了高功率系统中楔形光学元件的寄生反射引起的小尺度自聚焦效应,综合考虑了各个参数对纹波增长的影响。将反射光束与主光束的干涉叠加场进行了仔细分析,得出了干涉场在非线性增益介质中小尺度调制增益谱的表达式。针对小信号增益情形,数值计算了在钕玻璃片状放大器中,介质增益及传输距离改变的情况下小尺度调制的最大增益与放大器窗口楔角的变化规律。具体分析了放大器窗口的楔角与厚度对增益增长率的影响以及不同脉冲宽度的脉冲通过相同的窗口时,增益系数随脉冲宽度的变化关系。

Parasitic reflection is one of the most important fact impacts the laser′s near-field quality.Based on Bespalov-Talanov theory,the small-scale self-focusing caused by parasitic reflection and the parameter′s contribution to the growth of ripple in wedged optical device of high power system are discussed.By analyzing the interference field caused by the main beam and the reflected beam,the expression of small-scale modulated gain spectrum in no-linear media is found.The laws that the maxium gain of small-scale modulation grows with the window′s wedged angle of Nd-glass slab amplifier when the media gain or propagation distance changed are concluded.The influence of the length and wedge angle of amplifier window on the gain of perturbation is analyzed,additionally variation relation between the gain of perturbation and the width of the pulse with fixed window is derived.