Abstract

Raman spectroscopy can be used to characterize the crystalline phase composition (rutile/anatase) of single-layer TiO₂ optical coatings, multilayer TiO₂/SiO₂ coatings on reflective metals, and general all-dielectric TiO₂/SiO₂ structures such as high reflectors and Fabry-Perot filters. Measurements can be made in 1 second using diode array detection techniques or in a few minutes using a conventional scanning spectrometer. No special specimen preparation is required. The Raman technique contrasts markedly with conventional phase identification techniques such as x-ray and electron diffraction where extremely long counting times (about 24 hours) or difficult specimen preparation are always necessary and not always sufficient to produce the required resolution. Raman spectroscopy thus appears to be an excellent research tool for systematically understanding and optimizing optical properties, thermal stability and perhaps laser damage resistance in TiO₂ coatings, which are generally two-phase mixtures of anatase and rutile.

© 1984 Optical Society of America