Development of 91 cm size gratings and mirrors for LEFX laser system

Abstract

We have developed large size diffraction gratings and flat mirrors for large size pulse compressor in LFEX laser system. The required size of grating is 1.8 m, and we use 2 segment system with 91 cm element gratings. The substrates of mirrors and gratings are made of newly developed fused synthetic silica glass for low thermal expansion. The coating on this fused silica substrates are made by the ion beam assisted deposition (IAD) process for low stress coating. The size of element grating is 91 × 42 × 9 cm, and the largest mirror is 86 × 43 × 9 cm. The grating was lured by a novel scanning beam interference lithography system (NanoRuler II) in Plymouth Grating Laboratory in USA. The diffraction efficiency of the grating is better than 95%, and the wave-front error is better than λ/3 at 632 nm.