Daniela I. Iriarte

General Expression for the Voigt Function That is of Special Interest for Applied Spectroscopy

The purpose of this work is twofold. First we obtain a series expansion for the Voigt function that is valid for all values of the dimensionless parameter a (a measure of the ratio between the Lorentzian and Gaussian widths). Furthermore, the resulting coefficients are independent of the generalized coordinate b (the wavelength measured in units of the Gaussian width). In the second place, we fit an experimental “shaped bell” curve to a Voigt profile using certain theoretical restrictions that relate the maximum height and the full width at half-maximum.

Solution of the direct problem in turbid media with inclusions using Monte Carlo simulations implemented in graphics processing units: new criterion for processing transmittance data

The study of light propagation in diffusive media requires solving the radiative transfer equation, or eventually, the diffusion approximation. Except for some cases involving simple geometries, the problem with immersed inclusions has not been solved. Also, Monte Carlo (MC) calculations have become a gold standard for simulating photon migration in turbid media, although they have the drawback large processing times. The purpose of this work is two-fold: first, we introduce a new processing criterion to retrieve information about the location and shape of absorbing inclusions based on normalization to the background intensity, when no inhomogeneities are present. Second, we demonstrate the feasibility of including inhomogeneities in MC simulations implemented in graphics processing units, achieving large acceleration factors ( approximately 10(3)), thus providing an important tool for iteratively solving the forward problem to retrieve the optical properties of the inclusion. Results using a cw source are compared with MC outcomes showing very good agreement.

Stark Widths and Oscillator Strengths of Xe III Lines (Part II)

Stark widths and relative oscillator strengths were measured for more than 130 Xe III spectral lines emitted in a pulsed capillary discharge. As usual, these parameters become attainable once the deconvolution of line profiles is performed. In particular, 4f?6d, 5d?4f, 5d?6p, 6p?6d, 6p?7s and 6s?4f Xe III transitions have been considered. Extensive configuration interaction (CI) along with least-squares fitted atomic parameters were combined in Cowan code calculations, in order to check the quality of agreement with experimental f-values. Comparisons alike, drawn between experimental Stark widths and Griems semiempirical approach, guarantee an agreement within a factor of two for the whole of the lines, given a proper choice of the Gaunt factor for each single transition.

Stark widths and oscillator strengths of Xe III lines

In order to test the reliability of the Configuration Interaction (CI) method to predict the atomic parameters viz oscillator strengths of complex ions, we measured the profiles of forth (40) strong 6s-6p transitions of Xe III emitted by a pulsed capillary discharge. After deconvoluting the experimental shapes, Stark widths and relative oscillator strengths were obtained. When Least Square Fitted parameters were used in addition to extensive CI (CI + LSF), the agreement between theory and experiment for the gfs is within a factor two for the whole of the lines. Concerning the widths, the semiempirical approach provides values also within a factor two when the Gaunt factor is taken to be g(x) ~ 0.30.

RADIATIVE MECHANISMS IN LASER-PRODUCED PLASMAS IN Xe

Abstract In the present paper the LPP in Xenon at nearly atmospheric pressure is studied by frequency as well as temporal resolved spectroscopy. Experimental evidence confirms that the radiative recombination in the aftermath of the laser pulse, is the main mechanism by which the plasma dissipates its energy. It is also evident that the plasma observed is heated after the laser pulse ends, by a radiative wave evolving from the laser spot which also provides electrons. The evidence is supported by a careful analysis of the temporal evolution of ionized species, by the temporal evolution of the spectral shifts of the line spectrum and its spectral width, and by a careful analysis of the continuum emitted after the line spectrum in the plasma during the initial time-stage.

Photorecombination to excited states of Xe in laser produced plasmas

Abstract In the present work, we report the frequency spectra of the continuum generated in a laser produced plasma of Xe, in the region 3000–5800 A. From these studies it can be concluded that we have identified the photorecombination thresholds (radiative recombination, RR) to the excited levels of Xe I and Xe II and some autoionizing resonances nl−El′ transitions where with nl we label bound levels and with El′ auto-ionizing levels are indicated.

An efficient screening approach to be used in plasma modeling and ion-surface collision experiments

In this work we show that the Layzer theory for atomic calculations provides a theoretical framework and also a powerful computational approach if correct rules for the calculation of the screening parameters are given. Using the virial as a model for potential energy and splitting of two-body operators as sum of onebody operators, a neat definition of screening is given, satisfying diverse physically indispensable properties. Many different experimental and theoretical results are reproduced with high accuracy, with no fitting procedure involving energy levels or numerical potentials. A C++ code and an executable file are available upon request.

Electron impact ionization cross-sections for atoms and ions: A semiempirical study of trends and regularities

SummaryAfter analyzing nearly a hundred of experimental data about single ionization cross-sections by electron impact, we have found a series of relations between the maximum of the cross-sections and the slope of the curve at low energies, depending 0on the state of the target: neutral or ion. From these relations, an expression is found that reproduces the shape of the cross-sections in all the energetic range of the projectile.

Study of inhomogeneities in turbid media: experimental and numerical results

Near Infrared diffuse transmission of light through tissue is a tool for noninvasive imaging for diagnostic purposes. Most of the research has been focused over breast cancer imaging; however, major efforts have been done in cerebral tomography and topography imaging, as well as small animal organs imaging systems. In this work, we investigate the transmitted light profiles when scattering and absorbing cylindrical inhomogeneities are submerged at different depths inside slabs of turbid media. We analyze the transilluminance profiles when the phantom is scanned using both, CW and time resolved detection. The study of the spatial profiles obtained with CW light, shows an apparently contradictory effect when the absorption coefficient of the inclusion is higher than that of the bulk. In this case, the intensity profiles displays a peak of higher intensity where the inclusion is located, as it would be expected for a less absorbing inclusion. The experiments were compared and analyzed with a theoretical model for cylindrical inclusions and Monte Carlo simulations implemented in a Graphic Processing Unit (GPU).

Retrieval of the optical properties in a semiinfinite three layers phantom: theory, experiments, and simulations

In this work we introduce a theoretical model for light propagation in multilayered, turbid cylinders with an infinitely thick bottom layer, which can be applied to the study of biological systems such as the human head. Our approach was validated with experiments on a three-layered phantom and with Monte Carlo simulations. We show that the absorption and the reduced scattering coefficient of the deepest layer can be retrieved within reasonable errors.