Tungsten oxide thin films injected with protons (HxWO3) during deposition were prepared on glass substrates using reactive direct-current magnetron sputtering in a mixture of argon, oxygen, and hydrogen gases. The as-deposited films were bronze. The amount of injected protons, namely the x-value in HxWO3, was estimated using the dispersion of the extinction coefficient (kappa). The dispersion was evaluated by analyzing the experimental spectra measured with spectroscopic ellipsometry and optical photometry using the model composed of a homogeneous tungsten bronze layer with an additional surface roughness layer. As a result of analysis, the x-value was estimated to be approximately 0.1. (c) 2006 Elsevier B.V. All rights reserved.