Second-order susceptibility determination by Fourier analysis

Abstract

The macroscopic tensor components of the nonlinear surface susceptibilityX ⁽²⁾_s of monomolecular organic thin films have been determined with high precision using Fourier analysis of signals obtained by polarization rotation of the incident fundamental radiation. Our analysis clearly shows the presence of three complex-valued susceptibility-tensor components and hence the inapplicability of Kleinman's conjecture for a thin film of rotational symmetry around the surface normal. The description of the susceptibility in terms of three tensor components of different phase and magnitude indicates that the usual description within the model of non-interacting rod-like molecules is insufficient to describe the optical nonlinearity of a well-organized Langmuir-Blodgett-type thin film.