Phase-mismatched degenerate four-wave mixing: Complex third-order susceptibility tensor elements of C-60 at 768 nm

We describe and analyze an ah-optical method to measure bath the magnitude and the phase of each (complex) element of the chi((3)) tensor that determines degenerate four-wave mixing in a thin isotropic film on a thick substrate. me use the method to characterize the chi((3)) tensor of a 10-mu m C-60 film (on a CaF2 substrate) for 110-fs pulses at 768 nm. Using a fused-quartz plate as the nonlinear standard, we find the two independent Maker-Terhune elements of chi((3)) to have magnitudes \c(1221)(-omega, omega, omega, -omega)\ = (0.44 +/- 0.03) X 10(-12) esu and \c(1122)(-omega, omega, omega, -omega)\ = (0.50 +/- 0.03) X 10(-12) esu and phase angles phi(1221) and phi(1122), whose magnitudes are 145 degrees +/- 17 degrees and 139 degrees +/- 10 degrees. (C) 1997 Optical Society of America.