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Two-photon processes based on quantum commutators
Publication . Fratini, F.; Safari, L.; Amaro, P.; Santos, J. P.; LIBPhys-UNL; DF – Departamento de Física; American Physical Society
We developed a method to calculate two-photon processes in quantum mechanics that replaces the infinite summation over the intermediate states by a perturbation expansion. This latter consists of a series of commutators that involve position, momentum, and Hamiltonian quantum operators. We analyzed several single- and many-particle cases for which a closed-form solution to the perturbation expansion exists, as well as more complicated cases for which a solution is found by convergence. Throughout the article, Rayleigh and Raman scattering are taken as examples of two-photon processes. The present method provides a clear distinction between the Thomson scattering, regarded as classical scattering, and quantum contributions. Such a distinction lets us derive general results concerning light scattering. Finally, possible extensions to the developed formalism are discussed.
Josefa d' Óbidos workshop from panel to canvas. Multianalytical approach to materials and technical evolution of the most significant Portuguese painting workshop of the 17 th century
Publication . Antunes, Vanessa; Valadas, Sara; Serrão, Vitor; Carvalho, Maria L.; Candeias, António; Mirão, José; Cardoso, Ana Matos; Pessanha, Sofia; Manso, Marta; LIBPhys-UNL; DF – Departamento de Física; Elsevier Science B.V., Amsterdam.
In this work we address the study of three groups painted by Josefa d' Óbidos (1630–1684) and by her father Baltazar Gomes Figueira (1604–1674). These painters were the most important pair working in the 17 th century in Portugal with a Proto-Baroque style and the materials and techniques used by their workshop are almost unknown. Analytical procedures employed to characterize the materials and painting techniques involve molecular spectroscopy with μ-Confocal Raman (μ-Raman) and Fourier Transform Infrared Spectroscopy (μ-FTIR) in combination with other complementary methods such as X-ray Fluorescence Spectroscopy (XRF), μ-X-ray diffraction (μ-XRD) and Scanning Electron Microscopy with Energy Dispersive spectroscopy (SEM-EDS). Results are compared with the instructions of the most significant coeval Iberian painting treatises, with influence on Óbidos workshop. Conclusions of this study bring the first insight on the materials used, technical procedures and evolution from panel to canvas of Óbidos painting workshop, particularly highlighting the work of Josefa d' Óbidos, the greatest female Portuguese painter of all times.
Reference-free measurements of the 1s2s2p 2 P1/2,3/2o →1s22s 2S1/2 and 1s2s2p 4P5/2→1s22s 2S1/2 transition energies and widths in lithiumlike sulfur and argon ions
Publication . Machado, Jorge; Bian, Guojie; Bian, Guojie; Paul, Nancy; Trassinelli, M.; Amaro, Pedro; Guerra, Mauro; Szabo, Csilla I.; Gumberidze, A.; Isac, J. M.; Santos, José Paulo; Desclaux, J. P.; Indelicato, Paul; LIBPhys-UNL; DF – Departamento de Física; American Physical Society
We have measured the widths and energies of the 1s2s2p2P1/2,3/2→1s22s2S1/2 transitions in lithiumlike sulfur and argon, as well as the energies of the forbidden 1s2s2p4P5/2→1s22s2S1/2 M2 transition in both elements. All measurements were performed with a double-flat-crystal spectrometer without the use of any reference line. The transition energy measurements have accuracies ranging from 2.3 to 6.4 ppm depending on the element and line intensity. The widths and the intensity ratios of the 1s2s2p2P1/2,3/2→1s22s2S1/2 lines have also been measured. These are reference-free measurements of transitions in core-excited lithiumlike ions and have an accuracy comparable to the best relative measurements. We have also performed multiconfiguration Dirac-Fock calculations of the widths, energies, and intensity ratios. An extensive comparison between existing experimental results and theory is performed, and Bayesian techniques are employed to extract the energy of the 1s2p24P1/2→1s22p2P1/2 transition in sulfur and identify contaminant transitions.
Diagram, valence-to-core, and hypersatellite Kβ X-ray transitions in metallic chromium
Publication . Zeeshan, Faisal; Hoszowska, Joanna; Dousse, Jean Claude; Sokaras, Dimosthenis; Weng, Tsu Chien; Alonso-Mori, Roberto; Kavčič, Matjaz; Guerra, Mauro; Sampaio, Jorge Miguel; Parente, Fernando; Indelicato, Paul; Marques, José Pires; Santos, José Paulo; LIBPhys-UNL; DF – Departamento de Física; John Wiley & Sons, Ltd.
We report on measurements of the Kβ diagram, valence-to-core (VtC), and hypersatellite X-ray spectra induced in metallic Cr by photon single and double K-shell ionization. The experiment was carried out at the Stanford Synchrotron Radiation Lightsource using the seven-crystal Johann-type hard X-ray spectrometer of the beamline 6-2. For the Kβ diagram and VtC transitions, the present study confirms the line shape features observed in previous works, whereas the K h β hypersatellite transition was found to exhibit a complex spectral line shape and a characteristic low-energy shoulder. The energy shift of the hypersatellite relative to the parent diagram line was deduced from the measurements and compared with the result of extensive multiconfiguration Dirac–Fock (MCDF) calculations. A very good agreement between experiment and theory was found. The MCDF calculations were also used to compute the theoretical line shape of the hypersatellite. A satisfactory agreement was obtained between the overall shapes of the experimental and theoretical spectra, but deviations were observed on the low- and high-energy flanks of the hypersatellite line. The discrepancies were explained by chemical effects, which were not considered in the MCDF calculations performed for isolated atoms.
Probing deep tissues with laser-induced thermotherapy using near-infrared light
Publication . Lopes, Alexandre; Gomes, Ricardo; Castiñeras, Marta; Coelho, João M. P.; Santos, José Paulo; Vieira, Pedro; DF – Departamento de Física; LIBPhys-UNL; Springer Verlag
Optically tunable gold nanoparticles have been widely used in research with near-infrared light as a means to enhance laser-induced thermal therapy since it capitalizes on nanoparticles’ plasmonic heating properties. There have been several studies published on numerical models replicating this therapy in such conditions. However, there are several limitations on some of the models which can render the model unfaithful to therapy simulations. In this paper, two techniques of simulating laser-induced thermal therapy with a high-absorbing localized region of interest inside a phantom are compared. To validate these models, we conducted an experiment of an agar-agar phantom with an inclusion reproducing it with both models. The phantom was optically characterized by absorption and total attenuation. The first model is based on the macroperspective solution of the radiative transfer equation given by the diffusion equation, which is then coupled with the Pennes bioheat equation to obtain the temperature. The second is a Monte Carlo model that considers a stochastic solution of the same equation and is also considered as input to the Pennes bioheat transfer equation which is then computed. The Monte Carlo is in good agreement with the experimental data having an average percentage difference of 4.5% and a correlation factor of 0.98, while the diffusion method comparison with experimental data is 61% and 0.95 respectively. The optical characterization of the phantom and its inclusion were also validated indirectly since the Monte Carlo, which used those parameters, was also validated. While knowing the temperature in all points inside a body during photothermal therapy is important, one has to be mindful of the model which fits the conditions and properties. There are several reasons to justify the discrepancy of the diffusion method: low-scattering conditions, absorption, and reduced scattering are comparable. The error bars that are normally associated when characterizing an optical phantom can justify also a part of that uncertainty. For low-size tumors in depth, one may have to increase the light dosage in photothermal therapies to have a more effective treatment.
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Entidade financiadora
Fundação para a Ciência e a Tecnologia
Programa de financiamento
5876
Número da atribuição
UID/FIS/04559/2013