Optical nonlinearities in As2Se3 chalcogenide glasses doped with Cu and Ag for pulse durations on the order of nanoseconds

We investigate the dependence of the nonlinear optical properties of Cu-doped and Ag-doped As(2)Se(3) glasses on the incident pulse-width at 1.064 microm using the Z-scan technique. In this work, 11.5-ns optical pulses from a Nd:YAG laser were compressed up to 1.6 ns by using stimulated Brillouin scattering in heavy fluorocarbon liquid. The measurement of the pulse-width dependence of the optical nonlinearities leads to the separation of an ultrafast Kerr nonlinearity and a slow (cumulative) nonlinearity such as a thermal nonlinearity. The measured values of the nonlinear refractive index and the nonlinear absorption coefficient of 4 at.% Cu-doped As(2)Se(3) glass (where the normal photodarkening effect is sufficiently suppressed) and 4 at.% Ag-doped As(2)Se(3) glass were proportional to the pulse width, showing that the cumulative nonlinearity is present in these two glasses. The cumulative nonlinearity of these doped glasses is larger than one of the undoped glass. The origin of such slow nonlinearity is presumably attributed to the photostructural changes inherent in chalcogenide glasses and is directly independent of one of photodarkening.