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.