Unpolar and polar holographic grating recording by circularly polarized light on photoanisotropic azobenzene Langmuir-Blodgett films

A comparative study of photo-induced optical anisotropy was carried out on Langmuir-Blodgett films prepaxed from five different amphiphilic azobenzene derivatives. The anisotropy was induced by a linearly polarized pump beam of an Ar-ion laser at gimel = 514 nm and monitored by a linearly polarized probe beam of a He-Ne laser at gimel = 633 nm. Large optical anisotropy up to 0.35 has been induced. Holographic gratings were recorded by two left circularly polarized beams of the Ar-ion laser and time evolution of the first-order diffraction efficiency of the probe beam was recorded in an automatic regime. In such a geometry, the spatial modulation of refraction index reaches 0.14. The experimental data is consistent with a model for a photo-induced collective chromophore realignment in the heterogeneous domain structure of the films studied. The influence of an electric field of the corona discharge on the grating recording process was also studied and polar diffraction gratings have been prepared by a spatially periodic photo-poling process.