The depolarization of linearly polarized light from a 0.6328 µ He-Ne laser backscattered from rough metallic surfaces and inhomogeneous dielectrics with known statistical properties has been measured. For the case where the wavelength λ is smaller than the rms height h and the scale size l of the metallic surfaces, or λ is smaller than the average size of the particles in the dielectrics, the results indicate that the backscattered depolarized component is caused only by multiple scattering. The polarized backscattered component arises from both single- and multiple-scattering processes. At normal incidence, the ratio of the depolarized- to-total backscattered power, D/T, is of the order of 10-3 and 10-2 for metals of characteristic slope h/l=0.1 and 0.14, respectively. This is at variance with predictions based on single-scatter theory that at normal incidence D/T should be zero for metals. As the angle of incidence ψ increases and the beam approaches grazing incidence, D/T rapidly approaches a value near unity and becomes relatively insensitive to the surface slope, h/l. For inhomogeneous dielectrics, D/T is the order of unity for 0≤ψ≤88°. The dependence of the normalized depolarized component, D(ψ)D(0), on ψ satisfies the empirical law [D(ψ)/D(0)] = cosmψ, where m < 1 for metals and m ≃ 1 for inhomogeneous dielectrics.
J. RENAU, P. K. CHEO, and H. G. COOPER, "Depolarization of Linearly Polarized EM Waves Backscattered from Rough Metals and Inhomogeneous Dielectrics," J. Opt. Soc. Am. 57, 459-461 (1967)