利用Kogelnik一维耦合波理论, 以及离散傅里叶变换, 分析光栅矢量相互正交, 且串联级联放置的两透射型体相位光栅对空域任意分布的连续激光光束的衍射特性; 讨论其对入射光束的空间低通滤波性能, 并具体模拟其对畸变高斯光束空间低通滤波的效果。结果表明, 利用体光栅优良的角度选择特性, 无须对畸变光束进行聚焦, 即可实现入射光束角谱域中的高频成分与低频成分的空间分离, 滤除畸变高斯光束中高频角谱成分, 使得衍射光束与未畸变光束在空域中的光强分布非常接近, 达到滤除畸变光束中杂散成分且保留有用成分的主要目的。这种方法有效地避免了聚焦型空间低通滤波, 如针孔滤波在针孔附近光强过高, 易致针孔周边材料损坏等不利因素, 有助于应用至高功率激光光束质量的优化。

Based on Kogelnik’s one-dimensional coupled-wave theory and dispersed Fourier transform, the diffractive characteristic of two pieces of volume phase gratings, which are cascaded and having orthogonal grating vectors for the continuous-wave (CW) laser beam, is analyzed. The cascaded gratings’ low-pass spatial filtering for CW laser beam is performed. And the performance of its filtering for deformed Gaussian laser beam is simulated. The results show that with the fine angular selectivity of volume grating, the component of the larger quantity in angular spectrum domain can be deleted directly without focusing the laser beam. The distribution of intensity of diffractive laser beam is similar to that of the undeformed one in spatial domain. So the low-pass spatial filtering for CW laser beam is realized. This novel method can eliminate the drawbacks of pin-hole filter, which focuses the laser beam, enhances its intensity in the focal plane, and probably damages the stuff vicinal to the pin hole. So it may take the role of the pin-hole filter, especially in the high-power laser field.