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 Confinement Fusion (ICF) research is requiring 240 cavity-end mirrors. The mirror design is based on 44-cm square highly-reflective (HR)-coated deformable substrates. Such large dielectric mirrors are using interference quaterwave stacks of SiO2 and ZrO2-PVP (PolyVinylPyrrolidone) thin films starting from sol-gel colloidal suspensions (sots). The colloidal/polymeric ratio of the ZrO2-PVP composite system has been optimized regarding refractive index value, Laser damage threshold and chemical interactions have been studied using FT-IR spectroscopy. Therefore a promising deposition technique so-called "Laminar Flow Coating" (LFC) has been associated to sol-gel chemistry for HR sol-gel coating development. The as-designed LFC-prototype machine has been used for coating solution wave deposition by transportation of a tubular dispense unit under the substrate flat surface. Thin-film so created by the solvent evaporation was then dried at room-temperature or using short wavelength UV-curing built-in station. Optimization of parameters such as optical layer number, coating uniformity, coating edge-effect, 1053-nm reflectance and laser-damage threshold is discussed. Demonstration has been made that this novel coating method is a competitive way for large-area optical deposition compared to dipping or spinning techniques. Association of sol-gel colloidal suspensions to LFC process appear to be a promising cheap way of producing high-power laser optical coatings.