基于激光非线性传输和频率转换理论, 研究了频率转换中基频光与三倍频光相位关系对光束近场带来的影响。结果表明, 三倍频光近场对比度急剧增加对应的基频光B积分比频率转换前基频光近场对比度急剧增加对应的基频光B积分要小很多, 在基频光B积分远小于1.8 rad时, 三倍频近场也会成丝分裂。这对神光III原型装置首束集成实验终端光学元件（FOA）出现的不寻常损伤作出了合理的解释。对实际工程中如何降低终端光学元件的紫外损伤风险有重要的指导作用。

Based on nonlinear propagation of laser and frequency conversion theory, the effects of the relationship between 1ω phase and 3ω phase on 3ω near filed were studied. The results show that the B-integral corresponding to the sharp increase of 3ω near field contrast was far less than that of 1ω, even the B-integral of 1ω is less than 1.8 rad, 3ω near field occurs filament. This explained the unusual damage in final optics assembly(FOA) in prototype experiments of SGIII. The results plays an important role in reducing the risk of UV optics damage in FOA.