Characterization of the fast component of the complex third-order nonlinearity and time response of bulk materials and waveguides

We report a simple method to measure the third-order nonlinear refraction a nd absorption of bulk materials and waveguides. This method relies on the n onlinear evolution of the spectral intensity and width of femto-second puls es, owing to self-phase modulation, according to a variable chirp introduce d before propagation through the nonlinear sample. We describe the experime ntal details, and we present a comprehensive numerical analysis of the disp ersive and the nonlinear effects that can influence the measurement. We als o extend the method to characterize the time response of the fast cubic non linearity. (C) 2001 Optical Society of America.