Determination of n2 by direct measurement of the optical phase

We determine the nonlinear refractive index, n(2), in an optical material through the direct measurement of the phase of an ultrashort optical pulse, using the technique of frequency-resolved optical gating. This method results in the accurate measurement of n(2), with the error dominated by the uncertainty in the fluence measurement. We measure n(2) in fused silica and in potassium dihydrogen phosphate at 804 and 402 nm. These results are consistent with those from previous measurements of n(2) in these materials, and the measured dispersion of n(2) in fused silica agrees with theoretical predictions.