Thickness and Refractive Index Measurement of a Lamina with a Michelson Interferometer*

A description is given of a modification of Foch’s method for precise measurement of the thickness and the refractive index of a lamina. White-light reflection fringes from the lamina are compared in a spectrometer with the fringes produced by a Michelson interferometer when one light path in the interferometer contains the lamina. Analysis and experiment show that the interferometer fringes may be brought into perfect register with the reflection fringes over the entire spectrum regardless of the dispersion of the lamina.