高功率激光系统中非线性热像的强度可能达到光学元件的损伤阈值,从而危及系统的安全运行。明确并避免引起最强热像大小的模糊斑,可以降低热像的破坏威胁。通过理论分析与数值模拟方法,研究了高功率激光系统中非线性热像光强与模糊斑大小的关系。根据角谱传输和Bespalov-Talanov小尺度自聚焦理论,推导出一定厚度非线性介质的热像光强表达式,得到了热像光强随模糊斑大小的变化规律,并用数值模拟结果进行了验证。结果表明,随着模糊斑尺寸的增大,热像光强先是单调增大,达到一最大值后单调下降;热像光强最大时对应的模糊斑大小基本上与由Bespalov-Talanov小尺度自聚焦理论决定的最快增长小尺度调制尺寸相同。

In high-power lasers, nonlinear hot image is likely to damage expensive optical components. The damage risk of hot image to optical components may be reduced by identifying and eliminating the obscurations which induce the most intense hot images. The relationship between intensity of nonlinear hot image and dimensions of obscurations has been investigated theoretically and numerically. According to the theory of propagation of light spectrum and the Bespalov-Talanov theory, an expression for intensity of hot image through thick nonlinear medium is derived; the relationship between intensity of hot images and dimensions of obscurations is investigated and verified by numerical simulation. It is shown that, the bigger the obscuration is, the more intense the hot image is, when obscurations reach a certain size which is approximately determined by the fastest growing spatial frequency of the Bespalov-Talanov theory, the hot image becomes the most intense one, for a bigger obscuration, the intensity of its hot image decreases.