Nonlocal effects in the nonlinear optical response of chiral molecules: Third-order nonlinear circular dichroism

Summary form only given. Although it was predicted as soon as 1967, third-order nonlinear circular dichroism has never been experimentally observed. In this paper, we investigate this phenomenon in a liquid of chiral molecules. We first perform a theoretical calculation including nonlocal effects in the nonlinear light-matter interaction that allows to get insight into the process and to obtain its order of magnitude. We then demonstrate experimentally the existence of such a third-order nonlinear circular dichroism with a ruthenium-tris(bipyridyl) salt that we have under its two enantiomeric (Δ and Λ) forms. Several experiments are carried out with a 1 kHz, 180 fs laser source: a one beam saturation experiment where a saturation of the circular dichroism is clearly observed and a pump-probe experiment. In the latter case, by modulating the polarization of the probe or of the pump from a left to a right circular one, we observe an intensity-dependent circular dichroism. All these experiments are shown to derive from the same nonlinear mechanism, namely a chiral signature in the optical Kerr effect. We furthermore show that our results are in good agreement with our theoretical calculation. Extension of this technique to time-resolved circular dichroism measurement is discussed.