Differential colorimetry: a tool for evaluation of chromatic interference pattern

One of the oldest and simplest techniques for determination of thin transparent film thickness is based on evaluation of the interference colors produced by the film. Even if its accuracy is limited and technique itself has been overcome by many advanced techniques it still plays non-interchangeable role in observing the moving thin fluid lubricant films. a computer- aided system for reconstruction of thin fluid film shape from chromatic interference fringes is presented conceptually and the parts of system are demonstrated. Quasistatic fluid films were generated in an experimental equipment working as a two- layer Fizeau interferometer. Chromatic patterns produced by Tolansky method were photographed and digitized. The CIELAB color difference equation was used for comparing interferograms with the digital color chart to determine the fluid film thickness. Three-dimensional mesh surface plots of film shape with high film thickness resolution were generated using techniques of image processing and computer graphics. The limitations and accuracy of the proposed system are discussed and its validity was checked by observing lubricant capability to create coherent lubricant film under various conditions.