Influence of leaky waves on free-electron-induced nonlinear reflection properties of highly doped n-GaAs layer at medium IR-wavelengths

A multi-layer structure was theoretically elaborated to characterize the free-electron-induced optical nonlinearity in a thin sheet of a multi-valley semiconductor-like highly doped n-GaAs at medium-IR wavelengths. The multi-layer structure was designed to enhance the electric field and hence the absorption process inside this thin highly doped n-GaAs layer. The field enhancement was due to the excitation of a leaky TM polarized waveguide mode. An adequate nonlinear propagation model was derived taking into account the energy balance equation of conduction electrons distributed between the Γ- and L-valleys of highly doped n-GaAs. The angular and intensity dependent reflection properties were analysed. The influence of the intervalley deformation potential ΛLL on the nonlinear reflection properties was highlighted. The optical sensitivity of the leaky mode structure could be increased by ten times with respect to that of a bulk structure: reflection variations as high as factor of 3 for an intensity of 1.5 MW cm-2 could be simulated for a doping density of 7.7×1018 cm-3.