Determination of the nonlinear optical susceptibility c(2) of surface layers by sum and difference frequency generation in reflection and transmission

The theor. investigation of sum and difference frequency generation in thin surface layers with rotational symmetry led to formulas which connected the generated light intensities to the surface 2nd-order nonlinear susceptibility tensor. A max. of 7 tensor components was detd. in the lowest symmetry case. Measurements in transmission were esp. useful since they allowed easy variation of both polarization and angle of incidence. Large signal enhancements are expected for total internal reflection geometries. A consistent set of c(2) tensor components for a thin layer of Rhodamine 6G adsorbed on fused SiO2 was found based on data from reflection and transmission measurements