The reflection of light at the interface between two transparent, homogeneous and optically isotropic media such that the angle of refraction is 45° has the following interesting consequences: (i) the interface relfectivity for the parallel (p) polarization is the square of that for the perpendicular (s) polarization; (ii) the angular deviation of the propagation direction upon refraction is equal to the polarization (or ellipsometric) angle ψ and (iii) the complex reflection coefficient for the ppolarization is stationary, in both magnitude and phase, with respect to small charges of the (refractive and/or absorptive) optical properties of either one or both media. Furthermore, it follows from (iii) that: (iv) reflectivity of the p polarization, considered as a function of the ratio of refractive indices of the two media, is at a maximum; and (v) changes of the absolute magnitude and absolute phase of the reflection coefficient for the s polarization, caused by small perturbations of the optical properties, can be measured directly by ellipsometry.
Journal of the Optical Society of America (1917-1983)
R. M. A. Azzam, "Consequences of light reflection at the interface between two transparent media such that the angle of refraction is 45°," J. Opt. Soc. Am. 68, 1613-1615 (1978)