Laser processing of sol-gel coatings

Laser irradiation was used to densify sol-gel-derived silica coatings on SiO sub(2) and Si substrates. Index of refraction, shrinkage, infrared spectra, composition, and hardness of laser- and furnace-fired samples were studied during the course of densification. The evolution of the composition and properties of the laser-fired samples were different than for furnace-fired samples. At approximately 35% shrinkage, however, the properties of both laser- and furnace-densified coatings were identical to those of fused silica. Part of the differences in evolution is shown to be due to the rapid heating and cooling which occurs during laser processing, which results in concomitant trapping of hydroxyl in the films.