A purely interferometric method is suggested by which known standard wavelengths in the visible part of the spectrum are used to determine new wavelength standards in the infrared. The application of the method of exact fractions to measurements made using a Fabry-Perot interferometer whose plates are coated with highly reflecting dielectric films is discussed. It is shown that the large phase corrections introduced by these films may be reduced to differential corrections if relative wavelength measurements are made near wavelengths for which the phase change on reflection is π. A method of experimentally determining both the differential correction and wavelengths at which the phase change of π occurs is suggested.
D. H. RANK and H. E. BENNETT, "Problem of Phase Variation with Wavelength in Dielectric Films. Extension of Interferometric Standards into the Infrared," J. Opt. Soc. Am. 45, 69-73 (1955)