ORIGIN OF THE RESONANT OPTICAL KERR NONLINEARITY IN CD(S,SE)-DOPED GLASSES AND RELATED TOPICS

After having reported preliminary results related to saturation, we fi rst theoretically consider the various mechanisms contributing to the resonant optical Kerr effect in Cd(S, Se)-doped glasses. We obtain the expression for the expected effective susceptibility in different pos sible cases. This nonlinearity is studied experimentally using optical -phase conjugation in the low-intensity regime. We show that, by time resolving the nonlinear response of such glasses having experienced va rious degrees of photodarkening, we can clearly assess the origin of t he resonant optical Kerr effect in these materials. Usually, a combina tion of a fast free-carrier contribution due to particles without trap s and of a slow trapped-carrier one due to particles with traps is obs erved. For the free-carrier contribution, induced absorption is observ ed to be almost as important as absorption saturation. We also report frequency-dependent measurements and discuss the change in absorption spectrum and the increase of the nonradiative decay rate that accompan y darkening.