Low-pass spatial filter for laser beam based on cutoff filters

Due to the fine optical characteristics of cutoff filter, the configurations based on two pieces of long-pass cutoff filter or two pieces of short-pass cutoff filter were put forward respectively. Based on the geometrical optics, the performances of these two configurations were analyzed. The results show that the angular spectrum bandwidths of these two configurations depend on both the intersection angle between the cutoff filters and the angular bandwidth of transition zone. For the long-wave-pass cutoff filter, the intersection angle must be no less than two times of its cutoff angle. While for the short-wave-pass cutoff filter, the intersection angle must be no more than two times of its cutoff angle. Theoretically, its minimum bandwidth is equal to the angular bandwidth of transition zone, when the intersection angle is two times of the cutoff angle.