Using Hamming apodization technique to improve spectral beam combining efficiency of volume Bragg grating

Spectral beam combining technology of volume Bragg grating is an effective approach to obtain high-power laser output. The side lobe of output spectrum of volume Bragg grating is the main factor which limits the number of spectral beam combining. In this paper, the side lobe of volume Bragg grating was suppressed using Hamming apodization. The theoretical model of the refractive index of the one-dimensional apodized Bragg grating was built, and the diffraction characteristic of the Hamming apodized Bragg grating was analyzed, and the combining efficiency equation of the Hamming apodized Bragg grating was provided. Then the effect of apodized grating on the combining efficiency was analyzed. Numerical analysis shows that the side lobe in diffraction efficiency is suppressed well by using the Hamming apodization. The number of beam in spectral beam combining is increased from 13 to 20 in a total 20 nm bandwidth, and the combining efficiency can reach 75.3% after using Hamming apodized grating, while the output power is 1.5 times of the notapodized output power.