Degenerate four-wave mixing measurements on thin polymer films

We present a model for the description of a thin polymer layer as a set of noninteracting randomly oriented molecules in order to determine dependenci es between third-order nonlinear tensor components. The model results in di fferent numbers of independent tensor components for the three-dimensional and two-dimensional cases. Degenerate four-wave mixing measurements with di fferent angles of incidence were experimentally performed to check relation s between different tensor components in accordance with the sample thickne ss. Numerical calculations for diffraction in the Fraunhofer approximation were applied for degenerate four-wave mixing experiments on thin films in o rder to study the angle dependence of the signal beam. It was shown that th e distribution has vividly unsymmetrical character. The difference in the n onlinear tensor values between the traditional and the proposed procedure i s almost an order of magnitude.