Femtosecond interferometry for nonlinear optics

A technique of time‐resolved interferometry capable of observing nonlinear optical phenomena down to 70 fs is presented. We report the direct observation of the rotational contributions to the nonlinear refractive index of molecular liquids using this technique. The subpicosecond dynamics of such a nonlinearity in CS2 are investigated. This technique can be readily extended to solids, in particular laser glasses.