Transmission-mode perpendicular incidence ellipsometry of anisotropic thin films

We show that transmission-mode perpendicular incidence ellipsometry, which yields the trivial values Psi =45 degrees , Delta =0 for an isotropic thin film, can be used to provide useful data during the vacuum deposition of anisotropic coatings. Thus the number of quarter-wave film thicknesses necessary for a quarter-wave retardation plate can be determined simply by counting interference modulations on a Delta versus Psi graph, and the material property Delta n, the difference between the slow and fast axis refractive indices, is available from the gradient of a smoothed Delta versus thickness graph. The influences of differential absorption, differential refractive index inhomogeneity, and instrumental errors on the ellipsometric parameters are discussed.