Mueller-matrix Ellipsometry on Electroformed Rough Surfaces

Abstract

Automated Mueller-matrix ellipsometry was used to investigate the optical properties of electroformed standard rough surfaces as a function of r.m.s. surface roughness heights and angle of incidence. The r.m.s. roughness of the specimens examined varied from 50 to 12 500 nm. Six different surface finishes and 22 different specimens were examined and Mueller matrices were obtained at angles of incidence that varied from 30 to 80°. Measurements were conducted at a wavelength of 633 nm with the use of a division-of-amplitude photopolarimeter capable of simultaneously measuring all four Stokes parameters of arbitrarily polarized light. Values of ψ and Δ, the ellipsometric parameters, were derived from the measured Mueller matrices. The results demonstrate firstly the monotonic variations in the derived values of Δ with surface roughness for fixed angles of incidence, which include a ‘resonance’ effect for specimens with r.m.s. roughness heights close to the wavelength of light, secondly a systematic variation of ψ with the angle of incidence for different specimen roughness values and a reversal in these trends beyond the pseudo-Brewster angle, thirdly a monotonic variation in Δ values with the angle of incidence for different roughness values, fourthly relatively large variations in ψ values for roughness values close to the wavelength of light and fifthly relatively little change in ψ and Δ values for roughness values that greatly exceeded the wavelength of light.