Angular filtering by volume Bragg grating in photothermorefractive glass for nan

The two-dimensional angular filter based on volume Bragg gratings in photothermorefractive glass for a nanosecond (ns) laser pulse is demonstrated. The experimental results show that the near-field beam quality of the laser pulse was effectively improved. The near-field modulation and contrast ratio were improved by 1.75 and 4.48 times, respectively. The power spectral density curves showed that the spatial frequencies more than 0.9 mm?1 in the x direction and 1.2 mm?1 in the y direction were ef