A theoretical calculation is presented for third-harmonic generation in KDP crystal for type Ⅱ- type Ⅱ polarization-mismatch scheme by using the four-stepped Runge-Kutta method. For the “Shenguang Ⅱ” frequency tripling system, the doubling angle θd and the tripling angle θt are located at optimized situation, by changing detuned values of the polarization angle θp, the corresponding changes of pulse shape properties was gotten. The results show that when the polarization angle θp is located at optimized situation, the full width at half maximum (FWHM) τ is minimum and the pulse shape rises fastest. Increasing the θp from optimized situation causes the τ widens faster and the pulse shape rises slower than decreasing the θp from optimized situation. In the experiment, by changing the polarization angle θp, the pulse shapes consistency of the “Shenguang Ⅱ” eight frequency tripling beams has been accomplished. This work offers a method for adjusting crystals and actualizing power balance.

使用四阶龙格-库塔算法数值求解Ⅱ类-Ⅱ类偏振失配方案的三倍频稳态耦合波方程组。针对“神光Ⅱ”激光驱动器的三倍频系统，在二倍频匹配角θd和三倍频匹配角θt均处于最佳匹配情况下，以1°为单位改变偏振分配角θp的偏离量，得到对应的三倍频波形特性的变化。研究表明，偏振分配角θp处于最佳理论匹配位时，对应的三倍频波形半峰全宽最窄，且波形上升沿抬起也最快; θp从最佳匹配位增加比从最佳匹配位减小对应的半峰全宽变宽更快，对应的上升沿抬起更慢。根据所得理论结果，在实验中调节偏振分配角θp,达到了改变三倍频输出波形特性，进而实现八路三倍频波形一致的目的。该研究结果对于更快地实现激光驱动器装置的功率平衡有一定的应用价值。