The role of Bi2O3 on the thermal, structural and optical properties of tungsten-phosphate glasses

Glasses in the ternary system (70 – x)NaPO3-30WO3-xBi2O3, with x = 0–30 mol %, were prepared by the conventional melt-quenching technique. X-ray diffraction (XRD) measurements were performed to confirm the noncrystalline nature of the samples. The influence of the Bi2O3 on the thermal, structural, and optical properties was investigated. Differential scanning calorimetry analysis showed that the glass transition temperature, Tg, increases from 405 to 440 °C for 0 ≤ x ≤ 15 mol % and decreases to 417 °C for x = 30 mol %. The thermal stability against devitrification decreases from 156 to 67 °C with the increase of the Bi2O3 content. The structural modifications were studied by Raman scattering, showing a bismuth insertion into the phosphate chains by Bi–O–P linkage. Furthermore, up to 15 mol % of Bi2O3 formation of BiO6 clusters is observed, associated with Bi–O–Bi linkage, resulting in a progressive break of the linear phosphate chains that leads to orthophosphate Q0 units. The linear refractive index, n0, was measured using the prism-coupler technique at 532, 633, and 1550 nm, whereas the nonlinear (NL) refractive index, n2 was measured at 1064 nm using the Z-scan technique. Values of 1.58 ≤ n0 ≤ 1.88, n2 ≥ 10–15 cm2/W and NL absorption coefficient, α2 ≤ 0.01 cm/GW, were determined. The linear and NL refractive indices increase with the increase of the Bi2O3 concentration. The large values of n0 and n2, as well as the very small α2, indicate that these materials have large potential for all-optical switching applications in the near-infrared

A microstructured fiber with defined borosilicate regions to produce a radial micronozzle array for nanoelectrospray ionization

This work highlights the possibility of using microstructured fibres with predefined doped regions to produce functional microstructures at a fibre facet with differential chemical etching. A specially designed silica microstructured fibre (MSF) that possesses specific boron-doped silica regions was fabricated for the purpose of generating a radial micronozzle array. The MSF was drawn from a preform comprising pure silica capillaries surrounded by boron-doped silica rods. Different etching rates of the boron-doped and silica regions at the fiber facet produces raised nozzles where the silica capillaries were placed. Fabrication parameters were explored in relation to the fidelity and protrusion length of the nozzle. Using etching alone, the nozzle protrusion length was limited, and the inner diameter of the channels in the array is expanded. However with the addition of a protective water counter flow, nozzle protrusion is increased to 60 μm with a limited increase in hole diameter. The radial micronozzle array generated nine individual electrosprays which were characterized using spray current measurements and related to theoretical prediction. Signal enhancement for the higher charge state ions for two peptides showed a substantial signal enhancement compared to conventional emitter technology.Y. Fu, S. Morency, K. Bachus, D. Simon, T. Hutama, G. T. T. Gibson, Y. Messaddeq and R. D. Oleschu

Near-infrared Kerr nonlinearity of Pb(PO3)2–WO3 glasses

We report measurements of the nonlinear refractive index, n 2 , and the nonlinear absorption coefficient, α 2 , of Pb ( PO 3 ) 2 – WO 3 glasses. The measurements were performed using 100 fs (17 ps) laser pulses at 800 nm (1064 nm). Positive values of n 2 ∼ 10 − 19 m 2 / W and negligible α 2 were measured. The results show that the nonlinearity is faster than 100 fs and it is observed an increase of n 2 with the increasing of the WO 3 amount in the samples. The Boling, Glass, and Owyoung model, based on the semiclassical harmonic oscillator model, was used to predict the values of n 2 , with basis on the values of the linear refractive index of the samples

As ilhas, os arquivos e a história : o caso dos Açores

Nos Açores, a força da geografia define o carácter da história, que evidencia expressões bem diferenciadas. Por um lado, as ilhas agem como meio de aproximação dos continentes, equivalendo a um sinónimo de universalidade, que resulta de um privilegiado posicionamento no Atlântico Norte, movido pelo determinismo do mar e pelas condições da navegação à vela. Por outro lado, as ilhas figuram como factor de cristalização de comportamentos, correspondendo a um sinónimo de isolamento, motivado pelo afastamento do mundo e pela descontinuidade territorial interna. Nestas circunstâncias, os planos insulares de pesquisa histórica primam naturalmente pela pluralidade dos objectivos. Assim, demonstram uma participação muito activa na construção do mundo atlântico, que obriga à integração das investigações açorianas nas categorias mais universais do saber, mas aconselham também à realização de estudos de incidência local, conducentes à individualização de idiossincracias, que derivam da divisão do arquipélago em nove parcelas muito desiguais. Em 1979, por altura da publicação do seu livro O Arquipélago dos Açores no Século XVII: aspectos sócio-económicos (1575-1675), Maria Olímpia da Rocha Gil reconhece precisamente a indispensabilidade do desenvolvimento da investigação histórica açoriana de acordo com duas linhas ao mesmo tempo dissemelhantes e convergentes: “... em primeiro, aquela que nos leva a considerar que a história do arquipélago se integra no longo processo da história do Atlântico; em segundo lugar, a que se orienta para o estudo da evolução histórica local tendo em conta as características que lhe são próprias”. No entanto, desde tempos quase imemoriais, diversos cronistas e historiadores evidenciam um entendimento muito semelhante, que certifica a complexidade dos estudos históricos insulares. A comprová-lo, atentemos nas Saudades da Terra do Doutor Gaspar Frutuoso, redigidas logo no termo do século XVI, que relevam de uma assentada as especificidades locais, as correlações com os demais arquipélagos da Macaronésia e o envolvimento nas dinâmicas do Atlântico. [...

Femtosecond laser-written waveguides in thulium-doped fluoroindate glass for S-band amplification

Channel waveguides were written in a fluoroindate bulk glass containing thulium, with a femtosecond laser operating at 800 nm, 100 fs pulses and repetition rate 1 kHz. Formation of waveguides occurred for average powers from 1 to 8 mW (corresponding to energies of 1 to 8 microJ) and scan velocities in the range 0.1 to 4 mm/s. Passive optical characterization included visual inspection by optical microscope, insertion loss and mode profile. Active characterization was performed by co-propagating pumping in a dual-pump scheme that included a 808 nm and a 1054 nm laser diode for an efficient inversion of the $^3$H$_4$ level which is responsible for stimulated emission in the 1460-1530 nm spectral range. Preliminary tests show a net gain of 2.5 dB at 1487 nm, for straight waveguides 1 cm long. Applications include the fabrication of lossless components working in the S-band region of the optical communication spectrum

Bacterial Cellulose-Hydroxyapatite Nanocomposites for Bone Regeneration

The aim of this study was to develop and to evaluate the biological properties of bacterial cellulose-hydroxyapatite (BC-HA) nanocomposite membranes for bone regeneration. Nanocomposites were prepared from bacterial cellulose membranes sequentially incubated in solutions of CaCl2 followed by Na2HPO4. BC-HA membranes were evaluated in noncritical bone defects in rat tibiae at 1, 4, and 16 weeks. Thermogravimetric analyses showed that the amount of the mineral phase was 40%–50% of the total weight. Spectroscopy, electronic microscopy/energy dispersive X-ray analyses, and X-ray diffraction showed formation of HA crystals on BC nanofibres. Low crystallinity HA crystals presented Ca/P a molar ratio of 1.5 (calcium-deficient HA), similar to physiological bone. Fourier transformed infrared spectroscopy analysis showed bands assigned to phosphate and carbonate ions. In vivo tests showed no inflammatory reaction after 1 week. After 4 weeks, defects were observed to be completely filled in by new bone tissue. The BC-HA membranes were effective for bone regeneration

Novel fabrication process of planar waveguides in rare-earth doped fluoroindate glasses

We report the successful fabrication of planar waveguides in rare-earth doped fluoroindate glass substrates. A new procedure for waveguide fabrication using a thermally evaporated AgF nonmetallic film was developed. The refractive index changes of more than 0.03, associated to low propagation losses achieved, open new perspectives and show the potentiality of using this glass family toward further developments in fabrication and design of integrated optical devices for optical communication wavelengths

Clustering of rare earth in glasses, aluminum effect: experiments and modeling

Luminescent spectra of Eu3+-doped sol-gel glasses have been analyzed during the densification process and compared according to the presence or not of aluminum as a codoping ion. A transition temperature from hydrated to dehydroxyled environments has been found different for doped and codoped samples. However, only slight modifications have been displayed from luminescence measurements beyond this transition. To support the experimental analysis, molecular dynamics simulations have been performed to model the doped and codoped glass structures. Despite no evidence of rare earth clustering reduction due to aluminum has been found, the modeled structures have shown that the luminescent ions are mainly located in aluminum-rich domains. The synthesis of both experimental and numerical analyses has lead us to interpret the aluminum effect as responsible for differences in structure of the luminescent sites rather than for an effective dispersion of the rare earth ions. (C) 2004 Elsevier B.V. All rights reserved

Bulk photochromism in a tungstate-phosphate glass: A new optical memory material?

In this work, we present a new photochromic tungstate based glass which have both absorption coefficient and refractive index modified under laser exposure. The photosensitive effect is superficial under ultraviolet (UV) irradiation but occurs in the entire volume of the glass under visible irradiation. The effect can be obtained in any specific point inside the volume using an infrared femtosecond laser. In addition, the photosensitive phenomenon can be erased by specific heat treatment. This glass can be useful to substitute actual data storage supports and is a promising material for 3-dimensional (3D) and holographic optical storage.1251

Photoexpansion and photobleaching effects in oxysulfide thin films of the GeS2+Ga2O3 system

Oxysulfide systems undergo structural transformations upon illumination with laser light of near bandgap energy, as well as chalcogenide materials (glasses and films). In this paper, photoinduced effects such as photoexpansion and photobleaching were observed in GeS2+Ga2O3 (GGSO) films synthesized by electron beam evaporation. A surface expansion of the thin films and a shift to shorter wavelengths of the optical absorption edge were observed as a result of UV laser irradiation (wavelength of 351 nm) and they are dependent on laser power density, exposure time and film composition. These parameters were varied to evaluate and enhance the observed effects. In addition, the irradiated GGSO samples exhibited a decrease in refractive index, measured with a prism-coupling technique, which makes these films suitable candidates for applications as gratings and waveguides in integrated optics.FAPESP (05/58396-0