Study Of Surface And Bulk Scattering Of Transparent Substrates

Optical coatings play a very important role in modern optics, almost every optical system uses the technology of thin films. As for precise deposition techniques, the interfaces of optical coating are almost replica of the substrate surface. The quality of substrate surface has great effects to scattering of optical coatings, so it is important to measure and choose the surface quality of substrate before deposition.Generally speaking, as a nodestructive method to detect the surface quality, the method of light scattering possesses lots of advantages. Surface scattering and bulk scattering of transparent substrate are caused by surface roughness and refractive index inhomogeneity, they occur at the same time when light strikes the substrate, and it is difficult for them to be split for measurement. So a method to eliminate the bulk scattering in measuring transparent substrate surface is needed. The main research contents of this dissertation can be generalized as follows:Firstly, we use the electromagnetic field emit from one dipole in far area and first-order perturbation theory to set up the model of surface and bulk scattering of transparent substrates. Theoretically, angle-resolved scattering is got by solving Maxwell equations.Secondly, through the analysis of electric polarization angle difference between surface and bulk scattering by first-order perturbation angle-resolved scattering theory, we find the electric polarization angle between surface and bulk scattering is constant when incident and scattering angle are determined. So we can control polarization angle of polarizer and analyzer to eliminate surface scattering or bulk scattering. Thirdly, a method in theory is applied to eliminate bulk scattering of transparent substrates when scattering plane in the incident plane and polarizer angle is 45°. Through theoretical analysis and the numerical simulation, we get the analyzer angle in s-p plane. Thus, we obtain the independent surface scattering by eliminating the bulk scattering of transparent substrates.Finally, we design an experiment to validate our theory which is brought forward in this paper. We measure several silica substrates to get the total scattering by controling the anlayzer angle in s-p plane and find out the theory of eliminating bulk scattering of transparent substrate is valid, which lays a solid foundation in surface scattering measurement.