Theoretical Study on the Interferometry of Thin EHL Film Measurement

Interferometry has been widely utilized in elastohydrodynamic lubrication (EHL) film measurement since the 1960s. In-depth optical analyses are required to get more fundamentals of optical EHL film tests. In this paper, a stratified-layer model of optical EHL contact is numerically analyzed by the multi-beam interference approach. It is revealed that the high reflectance of the beam-splitter and the steel interface generate a deviation of the intensity profile from the two-beam interference. Previous experimental results about fringe contrast are reproduced, and the determination of the beam-splitter layer is theoretically clarified. Furthermore, some characteristics of spectrometry for ultra-thin film measurement are studied, and the dependence of the interference spectrum on the spacer layer thickness is displayed. The measurement simulation has theoretically confirmed the constant initial phase change assumed in practical measurement. It is theoretically demonstrated that in the spectrometry approach, TiO₂ layer can generate spectrum with high finesse and may be used in the future application. The theoretical results in this paper are correlated with previous experimental practices, and the optical EHL technique can therefore be much better theoretically understood.