Intensity and pure polarization holographic gratings in silica-based sol-gel thin films, containing carbazole group and Disperse Red 1, are obtained by photoisomerization at 488 nm and are investigated by means of the moving grating technique (MGT). General equations relating the modulated MGT signal to amplitudes and phase shifts of the index and absorption gratings are derived for thin films in the case of different polarization configurations. It is shown that the
technique, commonly used to characterize photorefractive gratings, is a powerful tool to investigate the orientation mechanisms responsible for the holographic polarization gratings formation.
Organic-inorganic films based on SiO<sub>2</sub>, containing Disperse Red 1 (DR1), carbazole units and 2,4,7-trinitro-9-fluorenone (TNF), have been prepared by a sol-gel technique. Diffraction gratings have been produced through different effects: photoinduced birefringence and photorefractivity, using 488.0 nm and 632.8 nm light, respectively. Pure polarization holographic birefringence gratings have been investigated and diffraction efficiencies higher than those obtained by light intensity modulation have been measured. The study of the temporal behavior of the diffraction efficiencies makes possible the identification of different processes involved in the DR1 molecular orientation: angular hole burning (AHB), angular redistribution (AR), Cis molecules gain has been determined by two-beam coupling (2BC) measurements. The effect of the polarization of the writing beams on the grating and of a circularly polarized photoisomerizing radiation during grating erasure has been interpreted in terms of an orientation contribution to the grating formation.
Nanocrystalline titania films were prepared by a complexing agent-assisted sol-gel dip-coating process. The effect of acetylacetone, diethanolamine and polyethylene glycol on the structure and morphology of the heat-treated titania films was examined by Raman and FTIR spectroscopy, x-ray diffraction and atomic force microscopy (AFM). The effect the complexing agents have on the anatase to rutile phase transition during the heat treatment process is studied. The understanding of this effect is expected to enhance our capacity to tailor the composition and morphology of films and thus their properties. The Raman and the infrared spectra of nanocrystalline titania films and the changes induced by the heat treatment were also investigated. We have studied the size of the crystallites in TiO<SUB>2</SUB> films and its dependence on the type of complexing agent used.
We report on a Raman study performed on sub-millimetric sized samples taken from the surface of a fresco painted in 1522-24 by Parmigianino (Girolamo Francesco Maria Mazzola, 1503-1540) in the second Chapel of the S. Giovanni Evangelista Church in Parma, Italy, whose restoration has been recently fully completed. The 'palette' of pigments used by the artist has been established. X-ray micro-fluorescence measurements confirm the results obtained by the micro-Raman technique.
Films of (alpha) -Fe<SUB>2</SUB>O<SUB>3</SUB>, whose high non-linear optical susceptibility (chi) <SUP>(3</SUP>) has been recently reported, have been prepared by the sol-gel method using two different sol-gel syntheses, both starting from inorganic salts as precursors, Fe(NO<SUB>3</SUB>)<SUB>3</SUB>-9H<SUB>2</SUB>O or FeCl<SUB>3</SUB>- 6H<SUB>2</SUB>O. Thermal treatments on films obtained by dip coating lead to the (alpha) -Fe<SUB>2</SUB>O<SUB>3</SUB> hematite structure for both preparations as indicated by XRD, Raman and X-Ray Absorption Spectroscopy measurements.