Fine structure in the χ(2) signals of inorganic-organic nanocomposites

Thin films of organically modified ceramics with nonlinear-optical-active chromophores produced in a sol-gel process exhibit Maker fringe signals which are superimposed by a periodic fine structure. The fine structure is shown to be due to Fabry–Perot resonances of the second-harmonic light which are stronger as compared to the amplitude corresponding to the regular Fresnel surface reflectivity by one to two orders of magnitude. The effect which is also observed on unpoled samples is tentatively ascribed to an accumulation and partial spontaneous orientation of the chromophores at the film surfaces.