Polarization Characteristics Of Layered Rough Surfaces

There are many substances with layered structures in nature,such as coated optics,coated aircraft,oil-spilled sea surfaces,snow-covered surfaces,etc.At the wavelength scale of light,the surface of each layer of medium can be regarded as random rough surfaces,and fully understanding the scattering and polarization characteristics of layered random rough surfaces is the basis for target detection.The Stokes vector plays an important role in polarization detection as a coefficient matrix that fully describes the polarization characteristics of light waves.Therefore,this thesis numerically analyzes the full-angle Stokes vector of scattered light from the layered random rough surface,and studies the influence of polarization state,incidence angle,refractive index,roughness and other factors on the components of the scattered Stokes vector.The specific work is as follows:1.The two-layer Gauss random rough surface is generated by Monte-Carlo method,and the light scattering of the double-layer random rough surface is analyzed based on the Kirchhoff approximation method,and the analytical expression of the scattering field at any point in space is obtained.An improved ray tracing method is proposed,the occlusion effect of random rough surface on light waves is calculated,the position of transmitted light from the upper layer reaches the lower layer,and the scattering coefficient of the layered rough surface obtained by simulation is in good agreement with the literature results,which proves the effectiveness of the method.2.The full-angle Stokes vector of the scattered light of Ti O₂ film and Si O₂ film on K9glass when the roughness of the random rough surface of the upper and lower layers is the same,when the S polarized light,P polarized light,45°polarized light and right-handed circular polarized light are incident at angles of 20°,30°and 40°respectively.The results show that the scattered light of linearly polarized light is still approximately linear polarization,the S polarized light and P polarized light in the incident plane maintain the original polarization,the45°polarized light becomes-45°polarization,other scattering directions and vibration directions rotate,and the scattered light of right-handed circular polarization is approximately changed to left-handed elliptic polarization.The increase of incidence angle has little effect on the polarization characteristics of scattered light,but the scattered light intensity of S polarized light,45°polarized light and circularly polarized light increases,and the scattered light intensity of P polarized light.Changes in the relative refractive index of the film and substrate do not affect the polarization characteristics of the scattered light.3.The Stokes vector of scattered light on the TiO₂ film and Si O₂ film at an angle of 30°is numerically analyzed when the roughness of the random rough surface of the upper and lower layers is different.The results show that the change of surface roughness of the upper layer has a greater influence on the components of the scattered light Stokes vector,and the change of roughness of the lower surface has a small effect,indicating that the light intensity and polarization state of the scattered light of the layered rough surface mainly depend on the scattering of the upper surface.