Near-field optical property of multi-layer dielectric gratings for pulse compressor

Abstract

Multi-layer dielectric gratings for pulse compressor in high-energy laser system must provide high diffraction efficiency. In addition, its laser induced damage property is critical for the system. Nonuniform optical near-field distribution of multi-layer dielectric gratings is one of the important factors to limit its laser induced damage threshold. Electric field distributions in the grating region and multi-layer film region are analyzed by using Fourier modal method. Effects of grating structure on peak magnitude of electric field in grating ridge are analyzed when the top layer material is HfO2 and SiO2, respectively. The results show that there exists an optimum top layer thickness, at which the peak magnitude of electric field within grating ridge is a minimum. And the peak electric field in the grating ridge can be reduced by designing top gratings with high aspect ratio structure when top layer thickness is increasing. Finally, the peak electric field in the grating ridge can also be reduced when the multi-layer dielectric grating is used at big incident angle.