The calculation of the optical depths of homogeneous plasmas: analytical, experimental, and numerical considerations.

Starting from the general expressions describing the line emission by a homogeneous plasma in local thermal equilibrium (LTE), in the approximation of Lorentzian shape of the line profile, a universal expression can be obtained relating the optical depth of the line to measurable quantities such as integrated line intensity, peak value, and full width at half-maximum (FWHM). This universal curve could be used for calculating the optical depth from experimental spectra without knowledge of the spectroscopic parameters of the emission line. Examples are given using experimental and computer-generated synthetic spectra.

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.

A new method for determination of self-absorption coefficients of emission lines in laser-induced breakdown spectroscopy experiments.

In this paper we present a new method for determining the self-absorption coefficients of emission lines in laser-induced breakdown spectroscopy (LIBS) experiments. With respect to other methods already present in the literature, the proposed approach has the advantage of not requiring, providing some conditions are fulfilled, any knowledge of the plasma parameters such as temperature and electron number density and of the emission line spectral coefficients such as transition probability. An example of the application of the approach is given for emission lines measured at different delay times after laser ablation of a silver target.