An instrument is described for measuring the thickness of thin liquid films by measurements of the irradiance in the reflected interference close to the central dark fringe. Variations in thickness can be measured by scanning a focused spot across the sample or an aperture across its image. The instrument has been tested on thin wedges.
L. R. Fisher,
N. S. Parker,
"Interference Method For Measurement Of Thickness Variations In Thin Liquid Films," Optical Engineering 19(6), 196798 (1 December 1980). https://doi.org/10.1117/12.7972613