Study On The Backscattering Enhancement Of Light From Randomly Rough Surfaces

Backscattering enhancement is important in rough surface scattering. This characteristic is manifested as a well-defined peak in the backscattering direction from the incoherent scattering component. This enhancement is applied in microwave, infrared, and visible remote sensing, as well as radar target detection, because it provides large amount of information on the target and background. The study of the characteristics of light scattering of rough metal surfaces is highly significant because of the special nature of dielectric properties when light is incident on the metal. The relative dielectric constant is complex, and the real part is negative. Moreover, the absolute value of the real part is much larger than that of the imaginary part. In this study, we focus on the backscattering enhancement of light scattering from strongly rough surfaces and weakly rough metal surfaces.First, second-order Kirchhoff approximation theory for light scattering from very rough surfaces is introduced. Scattering cross section with angular and propagation shadowing is also given. Angular distributions of incoherent scattering from the cross sections of rough metal surfaces and rough dielectric surfaces are calculated and compared. Thus, backscattering enhancement is caused by multiple scattering.The study focuses on backscattering enhancement of light from weakly rough metal surfaces. First, the mechanism of surface plasmon polaritons for weakly rough metal surfaces is discussed, and the dispersion relation is shown. Angular distributions of the mean differential reflection coefficient of the incoherent scattering component of weakly rough metal surfaces with the one-dimensional Gaussian spectrum, rectangular spectrum, two-dimensional Gaussian spectrum, and cylindrical spectrum are calculated by reduced Rayleigh equations and perturbation method. Results show that the surface plasmon polaritons can be excited for one-dimensional weakly rough metal surface only when the incident light is p-polarized, resulting in backscattering enhancement. An enhanced backscattered peak appears to some degree for both co- and cross-polarizations when the light is incident to the two-dimensional weakly rough metal surface. In addition, we analyze the influence of incident angle, roughness, and dielectric constant of the surface on the peak of the backscattering enhancement.Finally, characteristics of light scattering from a thin metal film and a dielectric film deposited on a perfect conductor, namely satellite peaks, in addition to the backscattering enhancement are discussed. We used the dispersion relation to provide the wave numbers of guided waves against the thickness of the layer. The relationship between the position of the satellite peaks and the wave numbers of the guided waves is explored. Angular distributions of the mean differential reflection coefficient are given using the perturbation method for multiplayer structures. The effect of thickness of the thin layer on the position and intensity of the satellite peaks are discussed in detail. In addition, the influence of incident angle, thickness of the thin layer, and dielectric constant on the backscattering enhancement is also analyzed.