Measurements of Lubricant Film Thickness by Optical Interference

Abstract

Optical interference is one of the most powerful tools for lubrication studies, since it enables in-situ measurements of lubricant film thickness under practical conditions. After various improvements, optical interferometry has been developed to apply not only to thick (e.g., micrometer-scale) films in hydrodynamic lubrication regime but also to thin (e.g., nanometer-scale) films in boundary lubrication regime. This paper reviews the principles of measuring lubricant film thickness by optical interferometry and some technical tips on methods using white-light spectroscopy.