SiO2–ORMOSIL double-layered broadband antireflective coating for high-power laser system

Broadband antireflective (AR) coating for high-power laser system has been realized by depositing double-layered SiO2–ORMOSIL thin films onto fused silica substrates. The refractive indices of bottom and top layers are 1.29 and 1.13, respectively. The top layer was composed of an ORMOSIL thin film which was prepared by a template-free sol–gel process by hybridization of tetraethoxysilane (TEOS) and dimethyldiethoxysilane (DDS). The hybridization of TEOS and DDS decreased gradually the refractive indices of ORMOSIL thin films from 1.21 to 1.13 as the molar ratio of DDS to TEOS increased from 0.0 to 0.8. The bottom layer was prepared by hybridization of acid-catalyzed and base-catalyzed silica sols. Finally, the double-layer broadband AR coating with transmittance of 100.0 and 99.9 % at 1064 and 532 nm, respectively, was realized. The laser-induced damage threshold (LIDT) of double-layer double-wavelength AR coating is 48.8 J cm−2. This double-layer SiO2–ORMOSIL AR coating possessed excellent transmittance at simultaneously 1064 and 532 nm, good AR stability and high LIDT, and will find important application in high-power laser system.