Optimization of the Optical Near-field Distribution of Metal Multilayer Dielectric Gratings for Pulse Compressors

Metal multilayer dielectric gratings (MMDGs) for pulse compressors used in high-energy laser systems should enable high efficiency, as well as provide broad bandwidths and high laser-induced damage thresholds. The non-uniform optical near-field distribution of MMDGs is an important factor that limits damage resistance capabilities. The efficiency and electric field distributions of MMDGs with a corrugated SiO2 layer and operated at 800 nm are analyzed by rigorous coupled-wave analysis. The maximum electric field in the grating ridge, match layer, and metal layer decreases with increasing grating diffraction efficiency. High efficiency and a low electric field are obtained with a 90 slope angle in the grating ridge. The bandwidth and maximum electric field in the metal layer decrease with increasing high-and low-index material pairs, and the maximum electric fields in the grating ridge and match layer initially decrease and then increase. The peak electric field in the grating is optimized with a merit function; the optimization covers the enhancement of diffraction efficiency, bandwidth, and reduction of electric field. The bandwidth of the optimized MMDGs is 160 nm with a diffraction efficiency exceeding 90%. The largest electric field is modulated in air to obtain a low electric field and high laser-induced damage threshold.