Thin films of lead titanate were prepared by a chemically modified sol-gel process and dip-coating technique. The process was refined such that homogeneous crack-free films could be produced which showed excellent waveguiding properties. A 600°C heat treatment was required to obtain the crystallization of the PbTiO3 perovskite phase. The microstructure of the phases was studied using waveguide Raman spectroscopy and transmission electron microscopy. The film was composed of an upper layer of large perovskite grains (∽100nm) on a lower lead content phase which appeared at the layer/substrate interface. This microstructure was related to lead diffusion into the substrate during heat treatment as shown by Rutherford backscattering spectrometry.

The different steps of thin film preparation by a sol-gel process are discussed: preparation of the starting solutions, control of the viscosity of the sol, deposition methods and thermal treatments. Transmission Electron Microscopy (TEM), Scanning Electron Microscopy (SEM) and Waveguide Raman Spectroscopy (WRS) are used to obtain structural characterization of the layers. The option of matrix doping is cited. Some optical properties of thin films using waveguide techniques and non-linear properties are underlined.

In this paper measurements of induced absorption and its dynamics in C60-doped solid xerogel matrices are presented. The measurements are performed in a pump-test geometry using picosecond pulses generated from a frequency doubled modelocked Nd:YAG laser. An induced absorption leading to optical limiting was observed. Outstanding optical limiting qualities for single shot excitation were found. Furthermore, limiting dynamics are studied. A decrease of the initial laser-induced absorption with a time constant of 150 picoseconds was observed. This is attributed to a transition from excited singlet to triplet electronic states in the C60 molecule. A long-living component due to the resulting triplet state population was also observed.

We present measurements of induced absorption and its dynamics in C60-doped solid xerogel matrices. The measurements are performed in a pump-test geometry using picosecond pulses generated from a frequency doubled mode locked Nd:YAG laser at 532 nm. We observe an induced absorption leading to optical limiting. We find outstanding optical limiting qualities for single shot excitation but some degradation above a certain threshold intensity for repetitive pulses. Below this degradation threshold, the material is stable and its limiting dynamics is studied. A decrease of the initial laser-induced absorption with a time constant of 150 ps is observed, down to a very long-lived constant level. We attribute this dynamics of induced absorption to a transition from excited singlet to triplet electronic states in the C60 molecule.

ZrO2 waveguides are prepared by the sol-gel process from a solution containing zirconiumn-propoxide and acetylacetone in propanol-2. Structural characterizations are investigated for different annealing temperatures using suitable techniques including Waveguide Raman Spectroscopy, Electron Microscopy and Atomic Force Microscopy. Films are amorphous at 300°C and the pure ZrO2 tetragonal crystalline phase appears beyond 400°C. Crystallized films present a dense, uniform and polycrystalline structure made up by randomly oriented nanocrystallites, the diameter of which increases from 38 Å at 400°C to 53 Å at 600°C. Waveguides are at least monomode TE0 at 632.8 nm. At this wavelength, optical losses are about, 0.8±0.2dB/cm for amorphous layers and increase up to 2.5±0.4 dB/cm for 600°C heat-treated waveguides.

Crack free, transparent and crystallized sol-gel derived PbTiO3 thin films were deposited on pyrex slide using the dip-coating technique. Both PbTiO3 and Pb2Ti2O7 phases were formed on monolayers whereas only pure PbTiO3 perovskite was observed when depositing multilayers. Films microstructure consisted of a dense and polycrystalline layer with grain size of about 80 Angstrom. Monolayers (about 120 nm thick) were monomode TE and TM with a refractive index around 2.01. Best optical waveguiding (over 10 mm) was achieved with monolayers when TM polarized light propagates and an optical loss of 7.5 +/- 0.8 dB/cm was measured for the TM(0) mode.

Wet acid-catalysed gels prepared by hydrolysis and condensation of tetramethylorthosilicate (TMOS) can be dried without the occurrence of fractures or cracks when drying conditions are appropriate. Furthermore, the resultant dried gel monoliths can be converted to silica glass on heating to 1100°C and holding there for 30 min when the composition of the starting solution is appropriate.

Silica gels doped with copper have been examined, after different heat treatments, by electron paramagnetic resonance (EPR) and nuclear magnetic resonance (NMR). A strong decrease of the Cu2+ EPR signal was observed for samples heated for 2 h at 650°C. After the same heat treatment, relatively intense sidebands due to the spinning at the magic angle appeared on each side of the 29Si NMR central line. These indicate a large broadening of the NMR lines, which confirm the recently observed ferromagnetism originating from Cu2+ ions.

Sol-gel derived PbO-TiO2 waveguides were prepared on pyrex substrates using the dip coating technique. Heat treatments conducted at 200 degrees C, 300 degrees C and 400 degrees C for one hour led to the densification of the layers and the increase of the refractive index values. The effect of water concentration in the precursor sol on the optical qualities of the waveguides is reported. Monolayer waveguides prepared with high water concentration provided the best coefficients of attenuation values (< 1 dB/cm). Preliminary study of Waveguide Raman Spectroscopy is presented.

We have investigated the dynamical processes of rare-earth photoluminescence in silica glasses produced by the sol-gel method. Generally, static spectroscopic properties are used as a tool to probe the local structure near dopants as well as for the study of glass formation. Rare earth ions are preferred structural probes, especially the Eu3+ ion for its sensitivity to local structural modifications and its spectroscopic simplicity. By an analysis of the decaying emission that follows a pulsed laser excitation, we have studied several dynamical processes. Importance of a distribution of different environments for the dopant is clearly seen even for the wet gels. The evolution of the lifetimes allow to study the densification process.

Monolayer monomode and multilayer multimode BaTiO3 waveguides have been prepared on amorphous silica substrates by using the dip-coating technique and the sol-gel process. After heat treatment, these waveguides were hard and of good optical quality (losses as low as 2.6 dB/cm were measured) but, their structure was found to depend strongly on the number of layers. Monolayer waveguides were totally amorphous even when heated at 1000°C, while multilayer ones exhibited the tetragonal BaTiO3 structure at an annealing temperature of 600°C.

In disordered fractal or nonfractal systems, the disorder induces rapid fluctuations of the acoustical vibrational wave functions, so that statistics can be used to resolve the problem of Raman scattering from localized low-energy vibrations. We derive the expressions of light-vibration coupling coefficient, C(ω), as a function of the frequency ω, in the case of the dipole-induced dipole mechanism of susceptibility fluctuation and for different types of correlation, from full correlation to no-correlation. The results are compared to the existing numerical calculations. The expressions of C(ω) are determined for other mechanisms of susceptibility fluctuations, depending on an interaction propagating in the fractal.

Comparison between low frequency Raman scattering and inelastic neutron scattering of amorphous polybutadiene shows that the light-vibration coupling coefficient is linearly frequency dependent. This agrees with earlier findings and we show here that it can be interpreted employing two different correlation lengths for the angular and radial correlations, under plausible approximations.

We have studied the magnetic properties of Cu-doped porous silica gels and found that the system seems to be ferromagnetic up to room temperature. This result is fascinating because the amount of Cu ranges from 0.15% to 3% in weight of the total sample. Magnetization, hysteresis loops, and EPR experiments are presented. The paramagnetic signal of the silica gel without doping is negligible. On the other hand, the analysis of the magnetic impurities by x-ray fluorescence shows that these impurities can account for only 10% of the magnetization observed at 300 K.

The effects of heat treatments on silica xerogels prepared from base-catalyzed hydrolysis and condensation of TMOS were studied by low-frequency Raman scattering and electron microscopy. Raman scattering measured in the range 3–700 cm−1 revealed a low-frequency band that arises from the discrete particulate character of base-catalyzed gels at very small size scales. A continuous evolution of the internal structure of particles is observed during thermal treatment and the Raman spectra are similar to the fused silica one at 1050°C. Electron microscopy observations of the nanostructure of the xerogels correlate with the particle Raman band maximum. The evolution of the sample as a whole (pores collapsing and densification) is described.

The effects of heat-treatments on silica xerogels prepared from base catalyzed hydrolysis and condensation of TMOS are studied by low frequency Raman scattering, scanning electron microscopy, small angle X-ray scattering and BET measurements. Raman scattering in the range 3-700 cm-1 reveals a low-frequency band that arises from the discrete particulate character of base-catalysed gels at very small scale. A continuous evolution of the structure inside particles is observed during the thermal treatment and the Raman spectra is similar to the fused silica one after treatment at 1050°C. Electron microscopy observations of the nanostructure of the xerogels correlate with the particle Raman band maximum. Complementary SAXS and BET measurements allows us to propose a model for the gel-to-glass transformation.

Recent works in our laboratories investigated the microstructure of titania films prepared from a colloidal solution and used as planar waveguides. The transmission electron microscopy including high resolution observations together with waveguide Raman spectroscopy, especially in the very low frequency range, showed a strong influence of the heat-treatment procedure on the films' morphology. In addition, atomic force microscopy provided valuable information on their surface roughness. At lower temperatures (450 degree(s)C), the films' structure consists of a mixture of amorphous TiO2 and anatase nanocrystals (4.5 - 5 nm) and its surface is smooth. On the contrary, when increasing the annealing temperature, the nanocrystals grow (50 nm at 1000 degree(s)C), pores (5 - 20 nm) are clearly distinguished and the films' waveguiding properties disappear. Here, we discuss the optical behavior of these films and its relationship to microstructure. It is clearly shown that a high degree of crystallization induces an important porosity, a rough surface and thus dramatically affects the films' waveguiding properties. Finally, we report a relatively simple strategy to stabilize the amorphous phase and control the crystallization in order to improve the optical quality of the waveguides.

Planar monomode TiO2:SiO2 waveguides were prepared by the sol-gel method from Liquicoat solutions supplied by Merck. Waveguide Raman spectroscopy was used to study TiO2:SiO2 thin films with different TiO2:SiO2 mixture ratios. The effect of annealing temperature on the microstructure of the films was followed up to 600°C. The amorphous phase crystallizes as anatase when the annealing temperature increases but Ti4+ ions remain in the silica network.

The sol-gel method has been used to prepare three different planar waveguides of low attenuation. The aim of this paper is to show that very low frequency waveguide Raman spectroscopy (V.L.F.W.R.S.) is useful for the characterization of thin film. The sample '' A '' is fabricated with a colloidal solution. It contains nanocrystals (anatase form) and amorphous TiO2. For the sample '' B '', the volume ratio of pure TiO2 and pure SiO2 in the starting solution is 1: 2. Its structure consists of TiO2 nanocrystals (rutile and anatase form) and SiO2 glass form. The sample '' C '' is prepared from a concentrated thorium phosphate solution and its structure is chain-like with certain interaction between chains. Samples elaboration is described in details. The electron microscopy results confirm the structural informations provided by V.L.F.W.R.S.