First, the phase differences between s- and p-polarizations of a circularly polarized heterodyne light beam reflected from the emulsion layer, and that from its substrate, are measured, respectively. The measured data are substituted into specially derived equations, so the refractive indices of the emulsion layer and its substrate can be calculated. Second, the variations of phase differences between s- and p-polarizations due to the wavelength shifts and the extraction of the holographic plate in a modified Michelson interferometer are measured. Then, the thickness of the emulsion layer and its substrate can be estimated based on the measured values of refractive indices, the wavelength shifts, and the phase difference variations. This method has some advantages, such as high resolution and easy operation in only one optical configuration.