Phase and frequency resolution of picosecond optical Kerr nonlinearities

We report on a method aimed at measuring both the real and imaginary parts of the third-order Kerr-type nonlinear-optical susceptibility of isotropic materials. It is based on Kerr ellipsometry in which analysis of the polarization state of transmitted light between a nearly crossed polarizer and an analyzer allows separation of pump-induced dichroism and birefringence. The method provides a natural measurement of nonlinear phase retardations in angle units, without any calibration procedure. By using a white-light continuum as a probe, this property is used to get a simultaneous measurement of the nonlinear dispersion in the whole visible spectrum. It is illustrated in tetramethylsilane, where stimulated Stokes and anti-Stokes Raman contributions to the nonlinearity are observed.