Based on the theory of inhomogeneous thin films, a model for refractive index of stratified dielectric substrate is firstly put forward. The substrate can be divided into surface layer, subsurface layer and bulk layer in turn. Both the s urface layer and subsurface layer, whose refractive indices obey statistical dis tributions, are equivalent to inhomogeneous thin films. They can be separated in to N1 and N2 sublayers respetively which are regarded as homogenous thin films. Subsequently, theoretical analysis was carried out utili zing the characteristic matrix method of optical thin films. Numerical calculati on for optical properties of single layer dielectric thin films was carried out. The computing results indicate that microdefects in surface layer and subsurfac e layer of the substrate alter the equivalent refractive indices of the thin film and the substrate, which leads to the deviation of pseudo-Brewster angles and assembling reflectance from ideal conditions. Meanwhile, these microdefects change the propagation characteristics in thin film and substrate, as a result t he phase shift of reflection and phase difference deviate from ideal conditions. In addition, this model is also suitable for calculating the influence of micr odefects in the substrate on optical propertied of multilayer dielectric thin fi lms.

No abstract

A model for refractive index of stratified dielectric substrate was put forward according to theories of inhomogeneous coatings. The substrate was divided into surface layer, subsurface layer and bulk layer along the normal direction of its surface. Both the surface layer (separated into N 1 sublayers of uniform thickness) and subsurface layer (separated into N 2 sublayers of uniform thickness), whose refractive indices have different statistical distributions, are equivalent to inhomogeneous coatings respectively. And theoretical deduction was carried out by employing characteristic matrix method of optical coatings. An example of mathematical calculation for optical properties of dielectric coatings had been presented. The computing results indicate that substrate subsurface defects bring about additional bulk scattering and change propagation characteristic in thin film and substrate. Therefore, reflectance, reflective phase shift and phase difference of an assembly of coatings and substrate deviate from ideal conditions. The model will provide some beneficial theory directions for improving optical properties of dielectric coatings via substrate surface modification.