NONLINEAR OPTICAL-RESPONSE OF AMORPHOUS SIH

We have carried out laser-induced grating and nonlinear transmission measurements near the band pp of amorphous Si:H. The nonlinear four-wave mixing response deviated substantially from traditional third-order effects. An intensity dependence of less than cubic for the diffracted intensity was observed. The nonlinearity does not follow the absorption profile. An effective nonlinear susceptibility chi(3) = 5 X 10(-9) esu was found at 572 nm. The nonlinear transmission showed saturable absorption at low intensities, and induced absorption at high intensities. This behavior can be attributed to light-induced defects.