Room-temperature mirror preparation using sol-gel chemistry and laminar-flow coating technique

The CEA/DAM megajoule-class pulsed Nd:glass laser devoted to Inertial Confi nement Fusion (ICF) research will require 240 cavity-end mirrors. The appro ved laser design necessitates 42-cm x 46-cm x 9-cm highly-reflective (HR)-c oated substrates representing more than 50 m(2) of coated area. Prototypes of these dielectric mirrors were prepared with interference quaterwave stac ks of SiO2 and ZrO2-PVP (PolyVinylPyrrolidone) thin films starting from sol -gel colloidal suspensions (sols). Low refractive index material was based on nanosized silica particles and high refractive index coating solution wa s made of a composite system. The colloidal/polymeric ratio in the composit e system has been optimized regarding refractive index value, laser damage threshold and chemical interactions have been studied using FT-IR spectrosc opy. A deposition technique so-called "Laminar Flow Coating" (LFC) has been associated to sol-gel chemistry for HR laser damage-resistant sol-gel coat ing development. This novel coating method confirmed its main advantages co mpared to dipping or spinning processes: coating large flat square substrat es at room temperature with small solution consumption, good thickness unif ormity, weak edge-effects, induced stress-free coating, good optical proper ties and laser damage resistance fulfilling.