Large-area sol-gel optical coatings for the Megajoule Laser prototype

In the field of thin film coatings, sol-gel (SG) process is an alternative to the conventional Physical Vapor Deposition (PVD) techniques. Sol-gel process is particularly competitive on large-area or fragile substates by taking advantage of various liquid phase deposition techniques performed at room temperature and atmospheric pressure, coupled with the versatility of organo-metallic chemistry. Developed by the French Commission for Atomic Energy (CEA) since 1985 for its former high-power lasers generation, optimized sol-gel coatings proved also very resistant to laser energy. In 1998, THALES Angenieux (TAGX) was selected by CEA to provide all the sol-gel coatings dedicated to the French Laser MegaJoule (LMJ) prototype, named Ligne d'Integration Laser (LIL). In cooperation with Saint-Etienne Pole Optique et Vision (POV), TAGX initiated the building of a sol-gel technological platform (SGPF) aimed at demonstrating the feasibility of production of optical and functional coatings on large area substrates. A technology transfer was performed by CEA (Le Ripault) to TAGX focusing on the manufacture mainly of single-layer antireflective coatings (SLAR), but also of multi-layer AR-coatings and of multi-layered highly reflective (HR)-coatings. Since beginning of 2001 and using SGPF equipments, TAGX successfully coated within specificaitons and schedule most of the 300 optics required for LIL activation. After this 2 years 1/2 production campaign in pre-industrial conditions, we can now analyse the advantages of each deposition technique used, the repeatability of the several processes, and the performance of the various coatings.