采用均方根(RMS)梯度表征的随机相位屏描述光束的低频相位噪声;用随机相位扰动描述中、高频相位噪声,建立了波前相位畸变模型。以Ⅰ/Ⅱ类角度失谐KDP晶体的高强度三次谐波转换为例,详细研究了三次谐波转换过程中,基频光和三倍频光的波前相位畸变之间的定量变化关系。分析了三次谐波转换过程对聚焦光斑形态的影响。研究结果表明,三倍频光的焦斑半径随着基频光低频相位畸变的均方根梯度增大而明显增大,且在均方根梯度较大时,三倍频光的焦斑半径几乎与基频光相近。

The model of the phase perturbation was built up, where the root mean square (RMS) gradient and random phase perturbation were introduced to describe the low and the high frequency phase noise, respectively. The quantitative relation between the phase perturbation of the fundamental field and tripling field has been studied in detail. The influence of third harmonics generation on the focal spot of the tripling field has been discussed. The results of simulation indicate that the focal spot size of the tripling field increases with the RMS gradient of the fundamental field obviously and is nearly the same as that of the fundamental field when the RMS gradient is higher.