Waveguide Raman spectroscopy has been applied to the analysis of single-layer, refractory-oxide, thin-film coatings on fused silica. With the use of the film as a waveguide, the interaction of the laser probe beam with the film is maximized, and interference from the silica substrate is minimized. An amorphous film of Ta<sub>2</sub>O<sub>5</sub> was found to be an excellent waveguide, yielding an intense Raman spectrum. Even though polycrystalline films of Y<sub>2</sub>O<sub>3</sub>, ZrO<sub>2</sub>, HfO<sub>2</sub>,and ThO<sub>2</sub> were found to be poor waveguides, they still yielded Raman spectra containing useful structural information. Such Raman spectra showed that the ThO<sub>2</sub> film was initially in an unusual structural form, which spontaneously transformed into cubic ThO<sub>2</sub>. Even for films yielding relatively weak Raman bands, substrate Raman scattering was not a serious interference. Representative spectra are presented, along with a brief discussion of the requirements for coupling optical beams into films with large refractive indices.

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