Applicability of Phase Ray-Tracing Method for Light Scattering from Rough Surfaces

Abstract

Ray-tracing method (RTM) based on geometric optics is a convenient tool in radiative heat transfer by tracing the intensity during light scattering, absorption, and multiple reflections. Some recent studies employed a modified RTM to trace the field amplitude and phase during light scattering from rough surfaces. Because phase is included, this method will be called PRTM hereafter. PRTM works well for multiple reflections in thin films with smooth interfaces, but its applicability for prediction of radiative properties of rough surfaces has not been established. The present study compares both PRTM and RTM with Kirchhoff’s approach (KA) for one-dimensional rough surfaces. The elements of the Mueller matrix calculated from these methods are compared for both dielectric and highly reflecting surfaces. When the characteristic lengths of roughness are much greater than the wavelength, the three methods yield essentially the same results. For small characteristic lengths, PRTM predicts certain coherent peaks resulted from wave interferences. However, the predicted peaks by PRTM are always smaller than those by KA. In addition, PRTM fails to predict coherent peaks for some elements. Therefore, PRTM cannot accurately address the wave features of rough surfaces with small characteristic lengths, due to its inherent assumption of specular reflection at surface microfacets, adopted from geometric optics.