啁啾脉冲放大系统中空间滤波器小孔尺寸的设计

为了获得啁啾脉冲放大系统(CPA)中空间滤波器的小孔尺寸,可以利用傅里叶光学的方法和激光模式理论,通过数学上的合理近似和对能量频谱函数的数值积分,计算激光束中基横模和主要低阶横模的径向空间频谱与空间截止频率,并讨论以基横模的空间截止频率作为空间滤波器的截止频率的可行性,从而确定小孔光阑孔径的大小并得出一个具有普遍意义的结论,即小孔直径约取6.93倍衍射极限长度时,空间滤波器能够较好地滤去TEM00模以外其他横模的大部分高频能量成分,从而提高光束质量,此结果在实验上得到很好的验证。此外,以M2因子为基础,可以得到一个用以辅助描述空间滤波器滤波性能的光束质量改善因子B。

Study on the Pinhole Size in the Spatial Filter of the CPA System

To obtain the size of the pinhole in the spatial filter of the CPA system,Fourier transform and laser multimode theories are applied.And by means of reasonably mathematical approximation and numerical integration,the radial spatial frequency spectrum and the spatial close frequencies of the basic transverse mode and main low-order transverse modes are calculated.The feasibility of applying the close frequency of the basic transverse mode to determining the close frequency of the spatial filter is also discussed,thus the diameter of the pinhole is determined and a widely significant result is achieved.In conclusion,the pinhole,with the optimal diameter of about 6.93 times the diffraction limit length,can fairly filter the high frequencies of most transverse modes except for the TEM_(00) mode,so that the beam quality is ameliorated and this result is well verified in experiments.Besides,a beam qualityimproving factor called "B" based on M~2 factor to help describe the performance of the pinhole-lens spatial filter is introduced.