Directional Characteristics of Radiation Reflection on Rough Metal Surfaces with Description of Heat Transfer Parameters

Abstract

Directional distribution of bidirectional reflectance ρ for visible laser irradiation is investigated experimentally on rough metal surfaces. The reflection is found to be far from perfect-diffuse. Relationship of reflection characteristics and rms surface roughness Σ is not simple in case Σ is of an order of the wavelength of incident radiation. It is recommended to analyze the reflection characteristics on (ρ cos θ_R), where θ_R is the zenithal angle of reflection. What has been called 'off-specular' peak does not appear in this case. A reflection model for describing the directional distribution is presented for heat transfer applications. The model can evaluate the values of the specular component R_S and the perfect-diffuse component R_d of the hemispherical reflectance R_H for directional incidence. It is interesting that calculated values of the specularly reflected energy ratio (R_S / R_H) do not always fit with our impression on the specularity in the directional distribution of ρ.