Reflection, Transmission, and Phase Shift of Light at Imbedded Optical Films

Abstract

Reflectance and transmittance of polarized light at imbedded optical films are measured for films of different compositions and thicknesses. The reflectance/transmittance ratio of plane-polarized light from such films, whose reflectance equals the transmittance at normal incidence, can be varied from approximately 13 to 4 by rotating the plane of polarization. A method is described that permits measurement of differences of phase shift, between reflected and transmitted light, for optical films imbedded in dielectric media that are approximately homogeneous. Phase-shift differences were obtained for two different aluminum films. Whereas values approximately π/2 rad were expected, values of 106° and 74°, respectively, were found for light polarized parallel and perpendicular to the plane of incidence. The two interferograms, produced by light of these two polarizations, appear to be complementary. However, the two interferograms produced by either polarization and observed from opposite sides of the film are not complementary—thus indicating a variation of absorption of the film with optical-path difference.