Diffraction Characterization based on Zero-level Diffraction Grating Structure

Semiconductor laser external cavity spectral beam combining (SBC) technology has been proven to be an effective method to improve the beam quality and output power of the output beam. Diffraction grating is a key component in the external cavity spectral beam combining structure. In this paper, a rectangular diffraction grating with a diffraction efficiency of up to 95.77<sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">%</sup> of zero order is obtained by simulating the rectangular diffraction grating using the finite element method combined with the strict coupling equation and analysing the influence of parameters such as grating period, angle of incidence and duty cycle on the diffraction efficiency. Concurrently, the zero-order diffraction efficiency exceeds 90% within the incidence angle range of 20° to 40° and reaches a value greater than 92% within the visible wavelength range. Finally, the effect of different surface coverings (with different refractive indices) on the diffraction characteristics of the grating is analysed again. The study results can be applied to high power lasers to meet external cavity spectral beam combination requirements.