H. Mesnil

Application of classical models of chirality to surface second harmonic generation

Two classical models (Kuhn and Kauzmann) are extended to calculate the second-order nonlinear response of an isotropic layer of chiral molecules. Calculation of the various nonlinear susceptibilities (electric dipolar, magnetic dipolar, and electric quadrupolar) is performed and applied to the derivation of the second harmonic field radiated by the molecules. It is shown that the two models give strikingly different results about the origin of the chiral response in such experiments. Previously published results are analyzed in view of this calculation which allows to understand the different interpretations proposed. This calculation emphasizes the interest of surface second harmonic generation to access information about the microscopic origin of optical activity in chiral molecules.

Experimental observation of nonlinear circular dichroism in a pump-probe experiment

Abstract We present experimental evidence of nonlinear optical activity in a time-resolved pump–probe experiment carried out in a liquid of chiral molecules. By modulating the polarization of the probe or of the pump, we measure a variation of the circular dichroism (CD) induced by the pump. Application of these techniques to time-resolved spectroscopy of excited molecules is discussed.

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

Abstract 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.

Application of microscopic models of chirality to second harmonic reflection

Abstract Classical models of chirality are extended to calculate the second-order nonlinear optical response of an isotropic layer of chiral molecules. The one-electron approach and the excitonic coupling model give strikingly different results about the origin of the chiral component. Furthermore, it is possible to discriminate between local (electric dipolar) and nonlocal (magnetic dipolar and electric quadrupolar) contributions to the nonlinear optical activity when playing with the polarizations of the fundamental and second harmonic beams. Surface second harmonic generation experiments are performed to validate these calculations, with a femtosecond titanium–sapphire laser, in a two-photon resonant configuration. We study a stilbene with an asymmetric carbon which corresponds to a one-electron chirality, and a Troger base exhibiting an excitonic coupling. Both experiments show a very good agreement with the theory, and emphasize the interest of second harmonic generation to access information about the microscopic origin of optical activity in chiral molecules.

Nonlinear optical activity in chiral molecules: Surface second harmonic generation and nonlinear circular dichroism

Nonlinear optical activity in chiral molecules is investigated. We first examine the importance of the nonlocality of the light-matter interaction in optical activity and extend this concept to second-order (surface second harmonic generation) and third- order (nonlinear circular dichroism) nonlinear optical phenomena. Microscopic models are also discussed. Various phenomena derived from these considerations are demonstrated experimentally with specially-synthesized chiral molecules. To cite this article: F. Hache et al., C. R. Physique 3 (2002) 429-437.  2002 Academie des sciences/Editions scientifiques et medicales Elsevier SAS chiral molecules / nonlinear optical activity