Contrary to a common misconception, it is possible to carry out absolute wavelength measurements with a Fabry-Perot interferometer having dielectric coatings even with no preliminary knowledge of the dispersion of phase change upon reflection. The method involves only a trivial change from that described by Meissner in his classic article on interference spectroscopy. The origin of interferometric wavelength corrections for phase change effects is discussed to emphasize that it is not dispersion of phase change but rather dispersion of optical path which necessitates such corrections.
R. W. STANLEY and K. L. ANDREW, "Use of Dielectric Coatings in Absolute Wavelength Measurements with a Fabry-Perot Interferometer," J. Opt. Soc. Am. 54, 625-626 (1964)