Brewster’s Effect for Gaussian Beams in Gallium Arsenide

GaAs is the most prospective material for terahertz wave switching. The Brewster’s effect provides transparency regardless of the thickness of the switching element. Constructing the devices based on the is complicated due to the nearly sliding angle. It is about 74.4 degrees for a plane wave in GaAs. Most of the quasi-optical devices use Gaussian beams. The accurate calculation with the recently developed numerical method shows that for a tightly focused beam with the radius of about the wavelength, the effective Brewster angle corresponding the minimum of reflection can decrease down to about 2.5 degrees. Moreover, the Brewster effect should be re-defined since the angle of the minimum reflection is not equal to the angle of the maximum transmission, since the real semi-insulating GaAs has the loss tangent of about $10^{-4}$ in sub-terahertz band.