One of the oldest and simplest techniques for the determining the thickness of a thin transparent film is based on the evaluation of the interference colors produced by the film. Though its accuracy is limited and the technique itself has been superseded by many advanced techniques, it still plays an irreplaceable role in observing moving thin fluid lubricant films. A computer-aided system for the reconstructing the shape of a thin fluid film from chromatic interference fringes is presented conceptually, and parts of the system are demonstrated. Quasistatic fluid films were generated in an experimental apparatus operating as a twolayer Fizeau interferometer. Chromatic patterns produced by the Tolansky method were photographed and digitized. The CIELAB color difference equation was used for comparing interferograms with the digital color chart to determine the film thickness. Three-dimensional mesh surface plots of the film shape with high 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 a lubricant’s ability to create a coherent film under various conditions.
"Differential colorimetry: tool for evaluation of chromatic interference pattern," Optical Engineering 36(9), (1 September 1997). http://dx.doi.org/10.1117/1.601415