Héctor F. Ranea-Sandoval

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.

Temperature and electron density gradient in Xe laser produced plasmas, by spectral analysis

Abstract We have performed a spectroscopic analysis on laser produced plasmas in Xe at intermediates pressures (less than 1 atm), resolved both spectrally and temporally, also discriminating different regions of the plasma. This is produced by tightly focusing the radiation of a Q-switched Nd : YAG laser on a cell equipped with an observation window at right angles with respect to the laser. Our results confirm that there is a gradient in electron density in the plasma ball formed by the laser. This gradient almost defines at least two regions, an outer layer of higher electron number density, and an inner core of lower electron number density. The electron temperature gradient has the same sign. These conclusions are supported by evidence taken using the spectral results mentioned above.

Ionic assignment in Xe pulsed discharges by time‐resolved spectral analysis

Time‐resolved spectroscopy has been used in a Xe pulsed discharge. The analysis reveals a delay in the onset of emission which is characteristic of the ion, suggesting that this can be related to the time for exciting each ionization stage, for given discharge conditions. This lag is longer for higher ions. The delay determination was done characterizing it for several lines of each ion; only some are listed below. The results enable a characterization of all the nonclassified Xe lines which are known to lase in the visible and the near UV, as belonging to three different groups of ions. One has temporal lags which coincides with those of Xe iv well‐classified lines; the other two, each having longer time delays, are assigned as transitions in higher ions.

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).