Heterodyne Interferometry Applied to the Characterization of Acousto-Electro-Optic Light Modulators

When the electro-optic and acousto-optic effects are combined into a single device, the resulting acousto-electro-optic (AEO) modulator shows improved flexibility to overcome some limitations of the individual modulators or their cascade combinations. By using optical interferometry, it is possible to investigate the AEO modulator behavior as a function of this applied voltage. By this way, a lithium niobate AEO modulator is positioned in one of the arms of a Mach-Zehnder interferometer and operates at 62 MHz frequency, which constitutes the intermediate frequency of the heterodyne interferometer. Operating the AEO modulator in the acousto-optic small diffraction efficiency regime, the photodetected signal amplitude and phase are analyzed, and the induced phase shift, transmission curve and linearity response are obtained. The experimental results show good agreement with that expected from the coupled-mode theory. The possibility of linear control of the optical phase shift by the external voltage, from 0 to 2 p radians, is demonstrated.

Photorefractive two-wave mixing phase coupling measurement in a self-stabilized recording regime

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Stabilized photorefractive running holograms, with arbitrarily selected phase shift, for material characterization

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Relief grating induced by photo-expansion in Ga-Ge-S and Ga-Ge-As-S glasses

We report the fabrication of relief diffraction gratings recorded on a surface of photosensitive Ga10Ge25S65 and Ga5Ge25As5S65 glasses by means of interference of two UV laser beams at 351 nm. The diffraction efficiency (eta) of first diffraction order was measured. Atomic-force-microscope (AFM) was used to perform a 3D imaging analysis of the sample surface topography that shows the superposition of an imprinted grating over the topography of the glass. The change in the absorption edge and the refractive index has been evaluated and a structural approach of the relief grating on the glass surface has been discussed.

Strong and fast phase modulation for quantitative analysis of photorefractive gratings

A new approach for studying photorefractive gratings in two-wave mixing experiments by a phase modulation technique is presented. The introduction of a large-amplitude, high-frequency sinusoidal phase modulation in one of the input beams blurs the interference pattern and provides powerful harmonic signals for accurate measurements of the grating diffraction efficiency eta and the output phase shift rho between the transmitted and diffracted waves. The blurring of the light fringes can be used to suppress the higher spatial harmonics of the grating, allowing a space-charge field with sinusoidal profile to be recorded. Although the presence of such a strong phase modulation affects the beam coupling in a rather complicated way, it is shown that for the special case of equal intensity input beams, the effect of the phase modulation on eta and rho is reduced to a weakening of the coupling strength. The potentialities of the technique are illustrated in a study of refractive-index waves excited by running interference patterns in a Bi12TiO20 crystal. Expressions for the diffraction efficiency and the output phase shift are derived and used to match numerically calculated curves to the experimental data. The theoretical model is supported by the very good data fitting and allows the computation of important material parameters.

Holographic recording in [Sb(Po-3)(3)](n)-Sb2O3 glassy films by photoinduced volume and refraction index changes

Glassy films of 0.2[Sb(PO3)(3)]-0,8Sb(2)O(3) with 0.8 mum-thickness were deposited on quartz substrates by electron beam evaporation. A contraction in the film thickness (photoinduced decrease in volume) and photobleaching effect associated with a decrease of up to 25% in the index of refraction has been observed in the films after irradiation near the bandgap (3.89 eV), using the 350.7 nm (3.54 eV) Kr+ ion laser line with 2.5 W/cm(2) for 30 min. A loss of 30% in the phosphorus concentration was measured by wavelength dispersive X-ray microanalysis in the film after laser irradiation with 5.0 W/cm(2) for 1.0 h. These photoinduced changes in the samples are dependent on the power density and intensity profile of the laser beam. Using a Lloyd's mirror setup for continuous wave holography it was possible to record holographic gratings with period from 500 nm up to 20 mum and depth profile of similar to50 nm in the films after laser irradiation with 5.0 W/cm(2) for 1 h. Real-time diffraction efficiency measurements have shown that ultraviolet irradiation induces first a refractive index grating formation, and after this, the photocon traction effect takes place generating an irreversible relief grating. Diffraction efficiency up to 10% was achieved for the recorded gratings. 3D-refraction index measurements and atomic force microscopy images are presented. (C) 2004 Elsevier B.V. All rights reserved.

Photoinduced effect in Ga-Ge-S based thin films

Glassy films of Ga10Ge25S65 with 4 mu m thickness were deposited on quartz substrates by electron beam evaporation. Photoexpansion (PE) (photoinduced increase in volume) and photobleaching (PB) (blue shift of the bandgap) effects have been examined. The exposed areas have been analyzed using perfilometer and an expansion of 1.7 mu m (Delta V/V approximate to 30%) is observed for composition Ga10Ge25S65 exposed during 180 min and 3 mW/cm(2) power density. The optical absorption edge measured for the film Ge25Ga10S65 above and below the bandgap show that the blue shift of the gap by below bandgap photon illumination is considerable higher (Delta E-g = 440 meV) than Delta E-g induced by above bandgap illumination (Delta E-g = 190 meV). The distribution of the refraction index profile showed a negative change of the refraction index in the irradiated samples (Delta n = -0.6). The morphology was examined using a scanning electron microscopy (SEM). The chemical compositions measured using an energy dispersive analyzer (EDX) indicate an increase of the oxygen atoms into the irradiated area. Using a Lloyd's mirror setup for continuous wave holography it was possible to record holographic gratings using the photoinduced effects that occur in them. Diffraction efficiency up to 25% was achieved for the recorded gratings and atomic force microscopy images are presented. (c) 2005 Elsevier B.V. All rights reserved.

Oscillating holograms recorded in photorefractive crystals by a frequency detuned feedback loop

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Influence of processing parameters on nanomaterials synthesis efficiency by a carbothermal reduction process

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

A systematic study of transfection efficiency and cytotoxicity in HeLa cells using iron oxide nanoparticles prepared with organic and inorganic bases

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Crystallization and preliminary X-ray diffraction analysis of a class II phospholipase D from Loxosceles intermedia venom

Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)

Efficiency evaluation of ZrB2 incorporation in the MgB 2 matrix phase using high-energy milling

The present study suggests the use of high energy ball milling to mix (to dope) the phase MgB2 with the AlB2 crystalline structure compound, ZrB2, with the same C32 hexagonal structure than MgB 2, in different concentrations, enabling the maintenance of the crystalline phase structures practically unaffected and the efficient mixture with the dopant. The high energy ball milling was performed with different ball-to-powder ratios. The analysis of the transformation and formation of phases was accomplished by X-ray diffractometry (XRD), using the Rietveld method, and scanning electron microscopy. As the high energy ball milling reduced the crystallinity of the milled compounds, also reducing the size of the particles, the XRD analysis were influenced, and they could be used as comparative and control method of the milling. Aiming the recovery of crystallinity, homogenization and final phase formation, heat treatments were performed, enabling that crystalline phases, changed during milling, could be obtained again in the final product. © (2010) Trans Tech Publications.

Ce0.97Cu0.03O2 Nanocatalysts Synthesized via Microwave-assisted Hydrothermal Method: Characterization and CO-PROX Catalytic Efficiency

In the work presented here, Ce0.97Cu0.03O2 nanoparticles were synthesized by a microwave-assisted hydrothermal method under different synthesis temperatures. The obtained nanoparticles were tested as catalysts in preferential oxidation of CO to obtain CO-free H2 (PROX reaction). The samples were characterized by X-ray diffraction, transmission electron microscopy (TEM), electron paramagnetic resonance spectroscopy (EPR) and temperature-programmed reduction (TPR). X-ray diffraction measurements detected the presence of pure cubic CeO2 for all synthesized samples. TEM images of the Ce0.97Cu0.03O2 nanoparticles revealed that samples synthesized at 80°C are composed mainly of nanospheres with an average size of 20 nm. The formation of some nanorods with an average diameter of 8 nm and 40 nm in length, and the size reduction of the nanoparticles from 20 to approximately 15 nm is observed with increasing synthesis temperature. EPR spectra indicated that copper is found well dispersed in sample synthesized at 160°C, located predominant in surface sites of ceria. For samples synthesized at 80 and 120°C, the species are less dispersed than in the other one, resulting in the formation of Cu2+−Cu2+ dimmers at the surface of ceria. TPR profiles presented two reduction peaks, one below 400°C attributed to the reduction of different copper species and a second peak around 800°C attributed to the reduction of Ce4+→ Ce3+ species located in the volume of the nanoparticles. The peak related to the reduction of copper species shifts to lower temperatures with increasing synthesis temperature, i.e., the sample synthesized at 160°C is more easily reduced than the ones synthesized at 120 and 80°C. The nanoparticles showed active as catalysts for the CO-PROX reaction. The microwave-assisted method revealed efficient for the synthesis of Ce0.97Cu0.03O2 nanoparticles with copper species selective for the CO-PROX reaction, which reaches CO conversions up to 92% for the sample synthesized at 160°C.

Color tunability in green, red and infra-red upconversion emission in Tm3+/Yb3+/Ho3+ co-doped CeO2 with potential application for improvement of efficiency in solar cells

The preparation of Tm3+/Yb3+/Ho3+ co-doped CeO2 prepared by the precipitation method using ammonium hydroxide as a precursor is presented. By X-ray diffraction the materials show the phase-type of fluorite structure and the crystallite sizes were calculated by the Scherrer's equation. No other phase was observed evincing that the rare earth ions were inserted into the fluorite phase as substitutional or interstitial dopants. The microstrain calculated by the Williamson-Hall method do not show significant changes in their values, indicating that the inclusion of rare earths does not causes structural changes in the CeO2 used as a host matrix. All material showed intense upconversion emission at red and green region under excitation with diode laser at 980 nm. The color of emission changes from green to red with increasing excitation power pump. The materials showed suitable photoluminescent properties for applications as a laser source, solar cells, and great emitter at 800 nm. (C) 2014 Elsevier B.V. All rights reserved.