Reflection equivalence of inhomogeneous and uniaxially anisotropic dielectric films with optical axis normal to the film surface
A comparison between light reflection from inhomogeneous and uniaxially anisotropic dielectric films on isotropic and homogeneous substrates is carried out. The reflection from inhomogeneous and uniaxially anisotropic ultrathin films is analyzed using the equations obtained in a long-wavelength approximation. Numerical calculations based on rigorous electromagnetic reflection theory for inhomogeneous and anisotropic interference films are also realized. It is shown that in the case of the absorbing substrate the reflection properties of an ultrathin inhomogeneous dielectric film, the refractive index of which varies only in the direction perpendicular to the layer, are equivalent to the reflection properties of a uniaxially anisotropic ultrathin film, the optical axis of which is normal to the film surface. For interference films on absorbing materials such equivalency takes place only in the case of weakly inhomogeneous films. For dielectric films on transparent substrates it is generally lacking. Solely ellipsometric angles for inhomogeneous and uniaxially anisotropic ultrathin films are equal in the first order in the ratio of film thickness to wavelength.