Third-order nonlinear circular dichroism in a liquid of chiral molecules

We present the signature of optical activity in the third-order nonlinear response of a liquid of chiral molecules. The existence of a nonlinear circular dichroism is demonstrated on two enantiomers of ruthenium(II)tris(bipyridyl) by performing a one-beam experiment in which the polarization is modulated from right to left circular one. This technique is then extended to pump-probe experiments in which, by modulating the polarization of the probe or pump, we can measure a pump-induced circular dichroism on the probe. This technique opens up the possibility of observing dynamical processes related to the chirality on an ultrashort time-scale.