Deposition of laser antireflection coating by a silicate sol-gel process

Subject of study.SiO2 antireflection coatings on fused silica substrates for use with high-power pulsed lasers operating in the near infrared region are studied. Aim of study. A process for depositing antireflection laser coatings on fused silica substrates using the silicate sol-gel technique is developed. Method. The sol-gel process used herein is based on the well-known Stöber process, which can be used to generate homogeneous spherical silicon dioxide nanoparticles of a controlled size in a colloidal sol solution. The sol was prepared by mixing tetraethoxysilane, ethyl alcohol, and an aqueous ammonia solution. The coating was applied by immersing the samples and then removing them from the mixture at a controlled speed ("dip coating"). Main results. The basic parameters of the sol preparation, coating application, and heat treatment processes are described. The excellent characteristics of the coating samples (transmittance, absorptance, and laser damage threshold) illustrate the functional capabilities of the process. The thickness and refractive index of the coatings were determined by analysis of the transmission spectra, and the film porosity was calculated using the Lorentz-Lorenz relation. Practical significance. Laser antireflection coatings deposited on fused silica substrates by the silicate sol-gel method support higher transmittance and laser-induced damage thresholds and permit the use of simpler, cheaper manufacturing equipment; coatings can be applied simultaneously to both surfaces of an optical element, and coatings can be applied to highly curved non-flat surfaces.