Design of high-efficiency multilayer dielectric film transmission gratings

The pulse compression grating is one of the core components of the chirped pulse amplification system, and its performance determines the performance and lifetime of the entire laser system. Previous studies have shown that the transmission grating is limited to a single material, and the groove depth of the grating is too deep to achieve high diffraction efficiency, making it difficult to fabricate. In this paper, a multilayer dielectric film transmission grating is designed for pulse compression. The grating with 1740 lines/mm and the central wavelength of incident light is 1060 nm. Six layers of dielectric films are added between the grating region and the substrate, with Ta₂O₅ (n=2.10) and SiO₂ (n=1.45) as high and low refractive index materials. The structure of the dielectric film transmission grating is optimized based on the Rigorous Coupled Wave Analysis (RCWA). The results show that when only considering diffraction efficiency, the - 1st order diffraction efficiency at a center wavelength of 1060 nm can reach 99.94% when the grating groove depth is 1.164μm and the duty cycle is 0.324; the -1st order diffraction efficiency in the wavelength range of 1042-1078nm can reach 95%. Through electric field analysis of the grating, an electric field enhancement phenomenon occurs at the grating ridge, with a maximum electric field intensity (normalized |E/E₀|) of 1.296. Then, the electric field and diffraction efficiency are optimized, resulting in a grating groove depth of 1.106μm, a duty cycle of 0.446, a -1st order diffraction efficiency of 98.26% at the center wavelength of 1060nm, and a -1st order diffraction efficiency of 95% in the wavelength range of 1038-1086nm. The maximum electric field amplitude is 1.183. The grating after modulation of the electric field increased the bandwidth from 36 nm to 48 nm, the diffraction efficiency decreased by 1.68%, and the maximum value of the electric field amplitude decreased by 8.71%.