A white-light interferometric thickness gauge has been developed that provides microinch sensitivity to gauge variations in moving transparent films. The new gauge that is suitable for on-line use can be adapted to monitor continuously the thickness profile of transparent films, the thickness of transparent coatings, and the birefringence of optically anisotropic materials. Its performance is relatively insensitive to variations in chemical composition, film temperature, haze level, and measurement geometry.
P. A. Flournoy, R. W. McClure, and G. Wyntjes, "White-Light Interferometric Thickness Gauge," Appl. Opt. 11, 1907-1915 (1972)