The reflectance of an absorbing substrate Rθ(ɸ) is considered as a function of the angle of incidence ϕ and an incident polarization parameter θ, where cos2θ and sin2θ give the power fractions of incident radiation that are p-and s-polarized, respectively. Taking GaAs as an example, we find that at certain wavelengths (e.g., 0.248 and 0.620 µm), the Rθ vs ɸ curve becomes oscillatory in a narrow range of θ > 45° with an unexpected secondary maximum appearing at oblique incidence. The extrema of the function Rθ(ɸ) are determined numerically, and their angular positions and reflectance levels are plotted vs θ for GaAs at photon energies of 1, 2, and 5 eV.
R. M. A. Azzam and A. M. El-Saba, "Reflectance of an absorbing substrate for incident light of arbitrary polarization: appearance of a secondary maximum at oblique incidence," Appl. Opt. 27, 4034-4037 (1988)