Near-field and far-field changes in the spectrum of light scattered from a randomly rough surface

Abstract

We consider the scattering of monochromatic and polychromatic light from a randomly rough dielectric film deposited on a planar, perfectly conducting surface. Setting up scattering integral equations with the image Green’s-function technique, we develop improved Monte Carlo simulations and use them to investigate the as yet unstudied evolution of frequency and angular spectra of the scattered light on propagation from the near to the far zone. In the monochromatic case, we illustrate the disappearance of the evanescent component and the formation of coherent enhanced backscattering and satellite peaks with increasing distance from the surface. In the polychromatic case, we find that the scattering of light from a rough surface produces significant spectral changes, which tend to increase on propagation from the near to the far zone. Coherent features in the intensity of the scattered light (such as satellite peaks), whose angular positions are frequency dependent, are found to cause very pronounced spectral changes in the scattered radiation. Since the existence and intensity of these coherent features are determined by the shape of the power spectrum of the surface roughness, and by the spectrum of guided or surface waves in the scattering system, we conclude that the frequency spectrum of the scattered light in different zones provides rich and physically meaningful information about the scattering system.