Abstract

Chiral molecules which have no plane and/or center of symmetry and occur as right or left handed enantiomers are of fundamental interest in chemistry and biology [1]. They are well known to display optical activity: ordinary rotation dispersion (ORD) and circular dichroism (CD). Recently, these linear optical characterizations have been extended to second order nonlinear optics, both at surfaces [2-8] and in liquids [9-10]. We focus here on polarization-resolved surface second harmonic reflection, which allows to measure nonlinear optical activity of thin layers of pure enantiomers by three different ways. First, the second harmonic polarization is analyzed for a p-polarized fundamental beam. Considering an isotropic film of chiral molecules, any rotation of the plane of polarization of the second harmonic beam compared to the p direction is characteristic of the chirality of the molecules. It is called ORD-SHG by analogy with the linear optical technique. Second (resp. third), the p- or s-polarization component of the second harmonic is measured for a right or left circular (resp. ± 45° linear) polarization of the fundamental beam. Here also, any difference is characteristic of the molecular chirality and is called circular difference or CD-SHG (resp. linear difference or LD-SHG, without any analogue in conventional linear optics).

© 2002 Optical Society of America