A fast (tau(response)< 90 fs) free-electron spin-flipping frequency-de
generate nonlinearity with a significant value of \chi(xxyy)((3)) (ome
ga, omega, omega, -omega) -chi(xyyx)((3)) (omega, omega, omega, -omega
)\ similar to 10(-8) esu has been observed in bulk gold at 1260 nm by
use of a nem pump-probe polarization-sensitive technique.