Fausto Osvaldo Bredice

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.

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.

Quadrupole distribution generated by a laser induced plasma (LIP) in air in earliest instants using pulses of 532 or 355 nm

The self-generated electric and magnetic fields in laser induced plasmas (LIPs) in air during the first 40 ns are experimentally investigated using different electric, magnetic and optical techniques. To produce LIPs we used the second and third harmonics (532 and 355 nm) of a Nd:YAG nanosecond pulsed laser with a range of irradiance from to W . The variation in time of the electric field was detected using the tip of a coaxial cable, and the spontaneous magnetic field (SMF) was measured using a probe. The spatial and temporal evolution of the plasma was studied using shadowgraphy and fast photography. It was observed that produced LIPs using pulses of 532 and 355 nm, generate plasmas of double core over the laser axis, while we observed that produced LIPs by pulses of 1064 nm are composed of a single core plasma. We found that the double-core plasmas have a quadrupole distribution of the charge, consisting of two oppositely directed dipoles which in turn correspond to each plasma core. The magnetic diagnostic showed an oscillating magnetic field azimuthal to the main axis of the double-plasma.

Dipolar distribution generated by laser-induced plasma (LIP) in air in earliest instants

We present an experimental investigation of the electric field potential and magnetic field generated by a laser-induced plasma in air, for time delays 0 ≤ t ≤ 50 ns. The laser used is a Nd : YAG, λ = 1064 nm, 10 ns at FWHM, and the irradiance applied is I = (1011–1012) W cm−2. We find that the collective effect of the charges in the plasma form a dynamic dipole distribution aligned with the laser beam axis. This experimental result is explained based on the mobility of the electric charges detected by mapping near the plasma with a coaxial cable probe. Shadowgraphy and fast photography techniques show that the plasma ionization front advances asymmetrically and mostly toward the lens. The intrinsic dipole moment is estimated by applying an external electric field. The magnetic diagnostic shows the presence of a current aligned with the laser beam that gives rise to an azimuthal magnetic field, corroborating the observed dipolar configuration.