Silvio Luiz Souza Cunha

Time-resolved optical Kerr-effect investigation on CS2/polystyrene mixtures.

The relaxation dynamics of carbon disulfide are investigated in mixtures with polystyrene (PS) using the time-resolved optical heterodyne-detected optical Kerr effect (OHD-OKE). The data are analyzed using both the model-dependent approach, which assumes four distinct temporal responses, and the model-independent Fourier transform approach, which generates a spectral response that can be compared with results obtained by depolarized Rayleigh scattering. A slow dynamics is observed for the OHD-OKE transient decaying exponentially with a time constant that varies from 1.68 ps for neat CS2 to 3.76 ps for the most concentrated CS2PS mixture. The increase of this time constant accompanies an increase in the viscosity of the mixture, so we can associate this component with the diffusive reorientation process of the induced polarizability anisotropy of the carbon disulfide in the mixture. The short-time nuclear response is characterized in the frequency domain by a broad band that peaks around 30 cm(-1) for neat carbon disulfide, and is associated with a complex relaxation pattern. The vibrational distribution shifts to higher frequencies when the PS concentration is increased in the mixture. This result is discussed in terms of an increase in the interaction strength between the PS phenyl rings and the carbon disulfide molecules.

Reflexões sobre o EAD no Ensino de Física

Some reflections on the use of the Information and Communication Technology (ICT) and the e-Learning in the teaching of the Physics are presented. In particular we discourse on the motivations, the conditions and the potential of the contribution of the e-Learning to the improvement of Physics teaching and learning.

DYE-INDUCED SPECTRAL NARROWING OF STIMULATED SCATTERING IN CS2

Abstract Narrowing of the super-broadened wings of both stimulated Rayleigh and Raman scattering spectral profiles in carbon disulfide (CS 2 ) has been observed in a liquid–core fiber system doped with 10 ppm of a dye (Coumarin 337). This effect is attributed to the light-induced pre-alignment of the anisotropic molecules of CS 2 , caused by the reorientation mechanism of excited dye molecules along the optical pump field. In addition, the enhancement of light-induced anisotropy in the presence of an absorbing dye has been observed in a light-induced birefringence experiment and is also explained in terms of the change in the guest–host interaction induced by optical excitation.

Characterization of ultrashort pulses by a modified grating-eliminated no-nonsense observation of ultrafast incident laser light E fields (GRENOUILLE) method

The measurement and characterization of ultrashort laser pulses remains an arduous task. The most commonly used pulse-measurement method is known as frequency-resolved optical gating (FROG), and another version with great experimental simplification and low-priced setup is known as grating-eliminated no-nonsense observation of ultrafast incident laser light E fields (GRENOUILLE). Nevertheless, there is interest in elaborating other, more accessible or simpler and cheaper, setups with equal or better assets. We explored modification of the GRENOUILLE method in which we replaced the original Fresnel biprism with a beam splitter and two mirrors and used a cheap webcam to measure the pulse traces. We have evaluated our system, and we propose a method to correct border effects caused by the beam intensitys profile based on the characterization of three pulse classes: Fourier-transform limited, double, and chirped. We compare the recovered electric field with further spectral and second-order correlation data of the corresponding pulses.

Aplicação de teorias cognitivas ao projeto de objetos de aprendizagem

Este artigo apresenta um conjunto de estrategias sendo utilizadas para otimizar o projeto e desenvolvimento de objetos de aprendizagem. Utiliza a teoria da carga cognitiva.

Molecular dynamics investigation with the time resolved optical Kerr effect on the CS2–C6H6 mixtures

An investigation of the molecular dynamics in pure liquids and in mixtures through the technique of time resolved optical Kerr effect is performed. The samples studied were the mixtures of carbon disulfide (CS(2)) with benzene (C(6)H(6)). The molecular dynamics of the pure liquids is briefly discussed while the main results are obtained for the mixtures. A slow dynamics component is observed for the optical heterodyne detected optical Kerr effect transient decaying exponentially with time constants on picosecond time scale. The fast subpicosend time relaxations are analyzed in terms of the nondiffusive component of the spectral response that is associated with the molecular dynamics. The modifications of the spectrum are quantified, and the explanation of the observed changes is given in terms of the structural interaction configurations that produced changes in the intermolecular potential within which the molecules execute librational motions.