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高能拍瓦激光的高精度脉宽测量对离轴抛物面镜焦斑功率密度的诊断以及光栅损伤阈值的分析都具有重要意义。分析了光束指向性和近场分布的周期性调制这两方面的误差影响。结果表明,当反射镜稳定性在5μrad时,光束指向性的误差最大为0.03%。当近场调制周期增加时,误差降低;而调制度增加时,误差增大。另外,采用镜像结构能降低近场缺陷导致的测量误差。当调制深度为1.5、调制周期大于10时,综合误差小于20%,最小可降至10%。镜像结构的误差均小于15%,最小可降至0。在拍瓦级激光脉宽测量实验中,证实了近场调制对于脉宽测量的影响及改善效果。
The high-accuracy pulse width measurement of high-power watt-lasers is of great significance to the diagnosis of focal power density of off-axis parabolic mirror and the analysis of grating damage threshold. The effects of errors on both the beam directivity and the periodic modulation of near-field distribution are analyzed. The results show that when the mirror is stable at 5μrad, the maximum error of the beam directivity is 0.03%. When the near-field modulation period increases, the error decreases; while the modulation increases, the error increases. In addition, the use of mirror structure can reduce the measurement error caused by near-field defects. When the modulation depth is 1.5 and the modulation period is greater than 10, the integrated error is less than 20% and the minimum can be reduced to 10%. The error of the image structure is less than 15%, the minimum can be reduced to 0. In the watt-level laser pulse width measurement experiment, the effect of near-field modulation on the pulse width measurement and the improvement effect are confirmed.