Laser densification of optical films

摘要

Sol-gel derived SiO$-2$/-TiO$-2$/ and WO$-3$/ films were densified with a CO$- 2$/ laser. Laser fired SiO$-2$/-TiO$-2$/ films had higher optical loss (6 dB/cm) than similar films fired in a furnace ($LS 1 dB/cm). For coating shrinkages up to about 40% the increase in refractive index during firing was similar for both laser and furnace fired SiO$-2$/-TiO$-2$/ coatings. At higher shrinkages both anatase and rutile were observed in the laser fired coatings. Loss measurements of laser fired samples in this and, likely, in previous studies were made in crystalline coatings. It is proposed that this, at least in part, is the cause of the high optical losses typically measured in laser densified silica-titania waveguides. The electrochromic coloring behavior of the WO$-3$/ films was examined using proton insertion. The coloring characteristics ($LS 20 s for 90% coloring) and bleaching characteristics ($LS 3 s for 90% bleaching) of laser fired WO$-3$/ films were comparable to the coloring and bleaching characteristics of high-quality sol-gel derived films fired in a furnace. Optimal coloring was obtained using moderate laser energy densities (approximately 50 - 100 J/cm$+2$/). This optimum occurred with less shrinkage than for furnace fired electrochromic films with similar coloring behavior.