Effect of protonation on the singlet-singlet excited-state absorption of meso-tetrakis(p-sulphonatophenyl) porphyrin

This work reports on the excited singlet-state absorption cross-section spectra of both biprotonated and\ud nonprotonated states of meso-tetrakis(p-sulphonatophenyl) porphyrin obtained by means of the Z-scan\ud technique with white-light continuum pulses. Although our main purpose was to determine these\ud photo-physical parameters in a wide spectral range, we also analyzed the role of accumulative effects\ud arising as consequence of the pulse chirp caused by the group velocity dispersion. This effect leads to\ud apparent changes in the measured excited-state absorption spectra, which can be corrected during the\ud fitting procedure to yield meaningful absorption cross-section values.FAPES

Excited state dynamics of meso-tetra(sulphonatophenyl) metalloporphyrins

The excited state dynamics of Zn2+, Fe3+, and Mn3+ meso-tetra(sulfonatophenyl) porphyrin complexes were investigated with a Z-scan technique at 532 nm using 70 ps and 120 fs single pulses and 200 ns pulse trains of a Q-switched and mode locked laser. We determined the characteristic interconversion and intersystem crossing times, quantum yields of the excited S1 state, and S1 → Sn and T1 → Tn transition cross-sections. The ground state cross-sections were obtained using UV−vis absorption spectroscopy, and a five-energy-level diagram was used to yield the photophysical parameters mentioned previously.FAPES

High-sensitivity optical humidity sensor based on a thin dielectric waveguide

A low-cost, high-sensitivity humidity sensor based on a low-loss dielectric thin film waveguide (WG) is presented. The guided mode is produced by coupling laser light into the film by optical tunneling through a solid gap deposited on the base of a semi-cylindrical lens. The light reflected from this optical system carries information about the refractive index of the medium neighboring the WG, and is detected by a low-cost CCD linear sensor and analyzed with a microcontroller or personal computer. The technique presents good sensitivity to relative humidity (RH) changes, especially below 10% RH, linear behavior between 20% and 80% RH, and a response time of a few seconds.FAPESPCNP

Ultrafast third-order optical nonlinearities of heavy metal oxide glasses containing gold nanoparticles

This work reports on the third-order nonlinear properties and the response time of GeO2-Bi2O3 glass, as well as the effect of gold nanoparticles on these properties. The nonlinear refractive index spectrum and the nonlinear absorption coefficient were determined by the Z-scan technique, and the response time was obtained through Kerr gate measurements, using femtosecond pulses. The results show that the presence of gold nanoparticles causes a saturable absorption effect that is overcome by the two-photon absorption process at higher light intensities, for wavelengths within the plasmon band. We measured a constant value for the nonlinear refractive index (n2) for the visible and infrared regions, which was not affected by the presence of gold nanoparticles in the sample. However, the n2 value is one order of magnitude higher than the one for fused silica and 1.5 times better than PGO (PbO-GeO2) glasses. In addition, the response time of the induced birefringence for the samples with and without gold nanoparticles is faster than the pulse duration (220 fs), indicating an ultra-fast electronic process.FAPESPCNPqCAPESINCT INF

Two-photon absorption spectrum in diazoaromatic compounds

This Letter studies the degenerate two-photon absorption (2PA) spectra of three diazoaromatic compounds using Z-scan with fs-pulses. The 2PA spectra exhibit resonant enhancement of the nonlinearity as the excitation approaches the linear absorption. The absence of 2PA to the ππ∗ band is related to the weaker donor/acceptor groups, and lower symmetry of diazoaromatic compounds, in agreement with our semi-empirical calculations. The higher magnitude of the 2PA cross-section, in comparison with single azoaromatics, demonstrates the positive effect of increasing conjugation. The decrease of 2PA cross-section with temperature is attributed to thermally induced torsions, which decreases the effective conjugation of diazoaromatic molecules.FAPESPCNPqCAPE

High-spin structure of 37Cl, intruder excitations, and the sd-fp shell gap

The structure of the N=20 nucleus Cl37 has been investigated in the Mg24(O16,3p) reaction with a 70 MeV O16 beam. A complex level scheme extended up to an excitation energy of 17 MeV and spins (29/2+) and (27/2−) on positive and negative parity, respectively, has been established. Lifetimes for the new states have been investigated by the Doppler shift attenuation method. Large-scale shell-model calculations have been performed in a valence space involving orbitals in the sd and fp shells using the sdfp and SDPF-M effective interactions. The comparison with the experimental data indicates the need for slight changes of the sd−fp energy gaps produced by these interactions.European Community FP6—Integrated Infrastructure Initiative—Romanian National Authority for Scientific ResearchINFNCNP

A simple method to measure critical angles for high-sensitivity differential refractometry

A total internal reflection-based differencial refractometer, capable of measuring the real and imaginary parts of the complex refractive index in real time, is presented. The device takes advantage of the phase difference acquired by s- and p-polarized light to generate an easily detectable minimum at the reflected profile. The method allows to sensitively measuring transparent and turbid liquid samples. (C)2012 Optical Society of AmericaBrazilian agencie Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)Brazilian agencie Fundacao de Amparo a Pesquisa do Estado de Sao Paulo (FAPESP)Brazilian agencie Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq)Brazilian agencie Conselho Nacional de Desenvolvimento Cientifico e Tecnologico (CNPq

Nonlinear optical characterizations of dibenzoylmethane in solution

This work reports on the two-photon absorption (2PA) cross-section and first hyperpolarizability of dibenzoylmethane solutions using femtosecond Z-scan and hyper-Rayleigh scattering techniques. The 2PA spectrum, spanning the wavelength range from 460 to 740 nm, presents a band centered at 510 nm, with a cross-section value estimated as 37 GM at this wavelength. Owing to the molecular symmetry, this band is not observed in the linear absorption spectrum. The sum-over-state approach was adopted to evaluate various spectroscopic parameters. Experimental and theoretical values of the first hyperpolarizability values were estimated in ethanol and DMSO solutions.FAPESPCNP

Remote Spectroscopy in the Visible Using Fibers on the Optical Internet Network

The work presented here demonstrates the feasibility of using the single-mode fibers of an optical Internet network to deliver visible light between separate laboratories as a way to perform remote spectroscopy in the visible for teaching purposes. The coupling of a broadband light source into the single-mode fiber (SMF) and the characterization of optical losses as a function of the wavelength are discussed. Sample spectra were measured with a portable spectrometer controlled by an acquisition program developed with the LabVIEW software that allows the data to be collected and analyzed.Fundação de Amparo à Pesquisa do Estado de São Paulo (FAPESP)FapespCNPqConselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq)CapesCoordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES

Synthesis of self-assembled tubes in direct conjugated porphyrin-gold nanohybrid solution

We report on the formation of self-assembled meso-tetrakis (p-sulfonatofenyl) porphyrin (H2 TPP'S POT. 4-''IND. 4') tubes stabilized by gold nanoparticles (NPs) in basic solution and on their spectroscopic chareterization. The role of the gold NPs in the aggregation dynamics of free-base sulfonated porphyrin (H2TPP'S POT. 4-''IND. 4') is also investigated. The direct conjugation of the gold NPs to the H2TPPS4 molecule quenches the fluorescence intensity, while absorption peaks are blue-shifted, indicating predominant H-type aggregation. It is observed that porphyrin molecules adsorbed on the surface of the gold NP interact and form tubes of maximum diameter ∼1.5 μm and length >100 μm. Steady-state and time-resolved spectroscopic techniques confirm nonradiative energy transfer from porphyrin to gold NP