Nonlinear circular dichroism in a chiral Ruthenium-tris(bipyridyl) solution

Chiral molecules which exist under two mirror-symmetrical configurations are known to play an outstanding role in many biophysical systems and therefore deserve a lot of attention from all domains in science. Utilization of optics has begun very early and optical activity (rotation of the light polarization or circular dichroism (CD) = difference of absorption for a right or a left circularly-polarized light) has provided a tool to characterize such molecules for a long time. Nonlinear optics has come to the study of chiral molecules only recently in surface second harmonic generation, demonstrating the sensitiveness of this technique to the chirality of molecules [1,2]. Second harmonic generation in a solution of chiral molecules has also been demonstrated unambiguously recently [3,4].On the other hand, third-order optics has not been so much developped. In particular, the Kerr effect, which is known to provide a host of valuable techniques to study the dynamics of molecules has never been utilized to probe chirality-related phenomena. In this paper, we demonstrate the existence of purely chiral effects in the Kerr response of a solution of chiral molecules. Experiments are two-fold: a one-beam experiment where saturation of the circular dichroism is unambiguously observed, and a pump-probe one, where the nonlinear circular dichroism spectrum is measured.