Induced grating autocorrelation measurement of the nonlinear refractive index of silica fiber

Using photorefractive beam coupling we demonstrate that the induced grating autocorrelation (IGA) technique is sensitive to the chirp and self-phase modulation (SPM) of an ultrashort optical pulse. In this technique, an IGA trace is produced by varying the delay between the two ultrashort excitation pulses that form a photorefractive grating and plotting the diffracted intensity of the probe pulse versus relative delay. From a series of IGA traces and numerical fits we obtain an average value of the SPM strength per watt in a silica fiber, from which we calculate a value for the nonlinear refractive index