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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 reflections are one of the important factors affecting the near-field quality of high power laser. Based on the Bespalov-Talanov theory, the small-scale self-focusing effect caused by parasitic reflection of wedge-shaped optical elements in high power system is analyzed emphatically. The influences of various parameters on the ripple growth are comprehensively considered. The interference superposition field of the reflected beam and the main beam is carefully analyzed, and the expression of the small scale modulation gain spectrum of the interference field in the nonlinear gain medium is obtained. For the case of small signal gain, the maximum gain of small-scale modulation and the wedge angle of amplifier window are calculated numerically when the gain and transmission distance of medium are changed in neodymium glass chip amplifier. The influence of the wedge angle and thickness of the amplifier window on the gain growth rate and the variation of the gain coefficient with the pulse width are analyzed in detail when the pulses with different pulse widths pass through the same window.