Design and simulation of near-field filtering for high power laser system

Diffraction characteristic of transmitting volume Bragg grating is analyzed with classical coupled wave theory, and the design method of transmitting volume Bragg grating is built. The near-field filtering effect is simulated with modulated super-Gaussian beam. The softening factor, near-field modulation and near-field contrast are used to analyze the beam quality. The power spectral density is used to describe the evolution of spatial frequency. The results show that the spatial frequencies from 0.3 mm-1 to 2.0 mm-1 are clean out with the near-field filtering, but the filtering effect is limited by the beam diffraction sidelobes of transmitting volume Bragg grating. (authors)