大型激光装置中的参数诊断系统需要使用缩束系统, 将被测脉冲转换为小口径光束, 以匹配相应的参数测量仪器。由于超短脉冲具有较宽的光谱, 因此在实际使用中会产生色散, 从而影响参数测量结果的准确性。分析了缩束系统的光学特性, 以及取样镜产生的群速度色散(GVD), 为诊断系统的设计提供依据。分析结果表明, 带楔角的取样反射镜与后续光路中使用楔形真空窗口构成了一对棱镜, 产生负的群速度色散。其数值与楔角的大小、传输距离成正相关。对于脉冲宽度大于50 fs的超短脉冲, 可以认为其脉冲宽度没有发生变化。这样就可以知道该参数诊断系统的工作范围。

It needs a down-collimator to convert big beams of a large laser facility into smaller beams in diameter to fit measurement instruments in diagnostic system. Because ultra-short pulses have wide spectrum, dispersion will be important to measurement. This paper provides some advice about diagnostic system designed by analyzing the down-collimator’s characteristic and group velocity dispersion of the sampling mirror. The result shows that the edged sampling mirror and the edged vacuum window can be treated as a pair of prisms, which generates negative group velocity dispersion. And the group velocity dispersion increases with the edged angle and the optical path. When input pulse width is above 50 fs, the output one will not change. So we can obtain the work range of this diagnostic system.