Reflectance of an absorbing substrate for incident light of arbitrary polarization: appearance of a secondary maximum at oblique incidence.

The reflectance of an absorbing substrate Rtheta(?) is considered as a function of the angle of incidence ? and an incident polarization parameter theta, where cos(2)theta and sin(2)theta 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 microm), the R(theta) vs ? curve becomes oscillatory in a narrow range of theta > 45 degrees with an unexpected secondary maximum appearing at oblique incidence. The extrema of the function R(theta)(?) are determined numerically, and their angular positions and reflectance levels are plotted vs theta for GaAs at photon energies of 1, 2, and 5 eV.