Experimental evidence of positive and negative nonlinear refractive index change in As/sub 2/Se/sub 3/

In this paper we present spatially resolved experimental observations of simultaneous presence of positive and negative nonlinear dephasing response in chalcogenide optical glass As/sub 2/Se/sub 3/. The technique is based on a pump/probe experiment using a Mach-Zehnder interferometer combined with a CCD camera where only one laser shot is needed to obtain a great number of measurement. The positive and negative nonlinear refractive index change in As/sub 2/Se/sub 3/ is discussed.