Broadband optical limiting in thin nanostructured silicon carbide films and its nature

Abstract

Broadband optical limiting of the ns laser radiation in visible and near IR spectrum range in nanostructured films of silicon carbide β-SiC(3C) studies are presented. The nature of the optical limiting mechanisms is discussed. The contributions of the optical nonlinear absorption and nonlinear scattering are determined and measured. It is shown that the nonlinear absorption is related to the two-step carrier excitation into the conducting band through the local levels in the band gap followed the absorption by nonequilibrium carriers. The mechanism of the nonlinear scattering is Rayleigh at its origin and arises as a result of difference of the refractive indices caused by the giant nonlinear refraction in nanocrystals of SiC and environment. It is shown that the Z-scan-like technique with the variable aperture size allows for combining contribution of both the nonlinear absorption and the nonlinear scattering mechanisms to increase the efficiency of the optical limiting.