Retrievals of a size parameter for phytoplankton and spectral light absorption by colored detrital matter from water-leaving radiances at SeaWiFS channels in a continental shelf region off Brazil

Many efforts are currently oriented toward extracting more information from ocean color than the chlorophyll a concentration. Among biological parameters potentially accessible from space, estimates of phytoplankton cell size and light absorption by colored detrital matter (CDM) would lead to an indirect assessment of major components of the organic carbon pool in the ocean, which would benefit oceanic carbon budget models. We present here 2 procedures to retrieve simultaneously from ocean color measurements in a limited number of bands, magnitudes, and spectral shapes for both light absorption by CDM and phytoplankton, along with a size parameter for phytoplankton. The performance of the 2 procedures was evaluated using different data sets that correspond to increasing uncertainties: ( 1) measured absorption coefficients of phytoplankton, particulate detritus, and colored dissolved organic matter ( CDOM) and measured chlorophyll a concentrations and ( 2) SeaWiFS upwelling radiance measurements and chlorophyll a concentrations estimated from global algorithms. In situ data were acquired during 3 cruises, differing by their relative proportions in CDM and phytoplankton, over a continental shelf off Brazil. No local information was introduced in either procedure, to make them more generally applicable. Over the study area, the absorption coefficient of CDM at 443 nm was retrieved from SeaWiFS radiances with a relative root mean square error (RMSE) of 33%, and phytoplankton light absorption coefficients in SeaWiFS bands ( from 412 to 510 nm) were retrieved with RMSEs between 28% and 33%. These results are comparable to or better than those obtained by 3 published models. In addition, a size parameter of phytoplankton and the spectral slope of CDM absorption were retrieved with RMSEs of 17% and 22%, respectively. If these methods are applied at a regional scale, the performances could be substantially improved by locally tuning some empirical relationships.

The effect of bulk light absorption on running photorefractive holograms

The influence of bulk light absorption on running photorefractive holograms is investigated. By solving the coupled wave equations we prove that the beam intensities, but not the beam phases, can be calculated by averaging the coupling constant over the crystal thickness. We show the importance of the effect by calculating the dielectric relaxation time at the crystal front, and from that the quantum efficiency from a feedback-controlled experiment with a 2.05 mm thick BTO crystal.We propose to simulate the effect of bulk light absorption by a rude estimate of the average dielectric relaxation time which is related in a simple way to the dielectric relaxation time at the crystal front, in doing so an error of less than 10% is introduced.

Decoration of Ti/TiO2 Nanotubes with Pt Nanoparticles for Enhanced UV-Vis Light Absorption in Photoelectrocatalytic Process

Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES)

Nanostructured TiO2-based composites for light absorption

Metal oxidenanocomposites were prepared by two different routes: polyol and sol-gel. Characterization by X ray diffraction showed that the first processproducesdirectly a two-phase material, while the sol-gelpowder never showed second phase below 600 degrees C. Light spectroscopy of the treated powders indicated similarities for the processed materials. Although the overall material compositions are about the same, different structural characteristics are found for each processing. With the exception of Ti-Zn materials, all the double metal oxide powders showed higher absorbance than either TiO2 powder.

Nanostructured TiO2-based composites for light absorption

Metal oxide nanocomposites were prepared by two different routes: polyol and sol-gel. Characterization by X ray diffraction showed that the first process produces directly a two-phase material, while the sol-gel powder never showed second phase below 600°C. Light spectroscopy of the treated powders indicated similarities for the processed materials. Although the overall material compositions are about the same, different structural characteristics are found for each processing. With the exception of Ti-Zn materials, all the double metal oxide powders showed higher absorbance than either TiO2 powder.

Upconversion of infrared-to-visible light in Pr3+-Yb3+ codoped fluoroindate glass

Bright fluorescence in the visible range has been observed in Pr3+-Yb3+ doped fluoroindate glass under infrared diode laser irradiation. The mechanism which contributes for the upconversion emission is identified and the energy transfer rate between Pr3+-Yb3+ is obtained for different concentrations. © 1998 Elsevier Science B.V. All rights reserved.

Giant non-linear absorption in Er3+-doped fluoroindate glass

Non-linear absorption is observed in Er3+-doped fluoroindate glass (in mol% 37InF2:20ZnF2:20SrF2:16BaF2:2GdF2: 2NaF:1GaF3:2ErF3) when the sample is irradiated with a CW laser emitting at 650 nm. An intensity dependence of the optical transmittance is detected. Saturation and sequential absorption of two photons are responsible for the decrease of 50% in the transmittance. The results are explained by simple models which are solved based on rate-equations for the populations of energy levels.

Nonlinear optical absorption of antimony and lead oxyhalide glasses

The optical limiting behavior and nonlinear optical properties of antimony and lead oxyhalide glasses were discussed. The large nonlinear absorption coefficients which range from 11 to 20 cm/GW was determined using standard Z-scan technique. The photodarkening in the samples were observed which suggested that they can also be useful for inscribing Bragg gratings using green lasers of moderate power.

Nonlinear absorption spectrum in perylene derivatives

Knowledge about nonlinear absorption spectra of materials used in photonic devices is of paramount importance in determining their optimum operation wavelengths. In this work, we have investigated the two-photon absorption (2PA) degenerate cross-section spectrum for perylene derivatives using the Z-scan technique with femtosecond laser pulses. All perylene derivatives studied present large 2PA cross-sections, only comparable to the best ones reported in the literature. The results achieved in the present investigation indicate perylene derivatives as promising materials for two-photon applications. ©2005 Optical Society of America.

Antimony glasses with large nonlinear refractive indices, small two-photon absorption coefficients and ultrafast response at telecom wavelengths

Nonlinear (NL) optical properties of antimony oxide based glasses (AG) were characterized for excitation wavelengths from 800 to 1600 m. The NL refractive indices, n2, and the two-photon absorption (TPA) coefficient, β, have been evaluated using the Z-scan technique. Values of n2≈ 10-15 - 10-14 cm2/W of electronic origin were measured and negligible TPA coefficients (β < 0.003 cm/GW) were determined. The response time of the nonlinearity is faster than 100 fs as determined using the Kerr shutter technique. The figure-of-merit usually considered for all-optical switching, T = 2βλ/n2 , indicates that AG are very good materials for ultrafast switches at telecom wavelengths. © 2007 IEEE.

Photo-Induced Dipole Relaxation Current in Natural Amethyst

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

Fabrication of coaxial TiO2/Sb2S3 nanowire hybrids for efficient nanostructured organic- inorganic thin film photovoltaics

Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)

A new beta-diketone complex with high color purity

In this work a new europium (III) complex with the following formula NH(4) [Eu(bmdm)(4)] was synthesized and characterized. The bmdm (butyl methoxy-dibenzoyl-methane) is a P-diketone molecule used as UV radiation absorber in sunscreen formulations. Coordination of this ligand to the Eu(3+) ion was confinned by FT-IR, while the Raman spectrum suggests the presence of NH(4)(+) ions. The photoluminescence spectra present narrow lines arising from f-f intra-configurational transitions (5)D(0-)(7)F(0,1,2,3,4), dominated by the hypersensitive (5)D(0)-(7)F(2) transition. In the spectrum recorded at 77 K, all transitions split into 2J + 1 lines suggesting that there is just one symmetry site around Eu(3+) ion. This symmetry is not centrosymmetric. The calculated intensity parameters are ohm(2) = 30.5 x 10(-20) cm(2) and ohm(4) = 5.91 x 10(-20) cm(2) for this complex. The CIE chromaticity coordinates (x = 0.67 and y = 0.32) show a dominant wavelength of 615 nm. The color gamut achieved by this complex is a 100% in the CIE color space. (c) 2005 Elsevier B.V. All rights reserved.

Langmuir-Blodgett films incorporating an ionic europium complex

Langmuir-Blodgett (LB) technique is a powerful tool to fabricate ultrathin films with highly ordered structures and controllable molecular array for efficient energy and electron transfer, allowing the construction of devices at molecular level. One method to obtain LB films consists in the mixture of classical film-forming molecules, for example Stearic Acid (SA) and functional metal complex. In this work NH(4)[Eu(bmdm)(4)], where the organic ligand bmdm is (butyl methoxy-dibenzoyl-methane) or (1-(4-methoxyphenyl)-3-(4-tert-butylphenyl)propane-1,3-dione) was used to build up Langmuir and LB films. Langmuir isotherms were obtained from (i) NH(4)[Eu(bmdm)(4)] complex and (ii) NH(4)[Eu(bmdm)(4)]/SA (1:1). Results indicated that (i) form multilayer structure; however the surface pressure was insufficient to obtain LB films, and (ii) can easily reproduce and build LB films. The dependence of number of layers in the UV absorption spectra suggest that the complex did not hydrolyze or show decomposition, UV spectral differences observed between the solution and the LB film indicate that the complex has a highly ordered arrangement in the film and the complex has an interaction with SA. Excitation spectra confirm a ligand-europium energy transfer mechanism. The transition lines of Eu(3+) ion were observed in emission spectra of all films, the photoluminescence spectra indicate a fluorescence enhanced effect with the number of LB layers. (C) 2009 Elsevier B.V. All rights reserved.

Structural studies in lead germanate glasses: EXAFS and vibrational spectroscopy

The Raman, IR absorption and EXAFS spectra at the Ge K-edge and Pb LIII-edge of eight lead germanate glasses, with general formula xPbO(1-x)GeO2 with x = 0.20, 0.25, 0.33, 0.40, 0.50, 0.53, 0.56 and 0.60, have been measured. The occurrence of [GeO6] units besides [GeO4] could not be deduced unambiguously from the data. The vibrational and EXAFS data agree with a progressive depolymerization of the network. Starting from all Ge atoms linked to four bridging oxygens in GeO2 (x = 0), the number of tetrahedral units with one or two non-bridging oxygens increases with x. At low content, Pb2+ ions act as modifiers in the germanate structure, but to a lesser extent than an equivalent number of alkaline ions. © 1993.