الفهرس 
IntroductionOnly 14 pages are availabe for public view
 |  | from | 114 |  |  |
| | | from | 114 | | |
Abstract
In order to improve the sensitivity and reproducibility of the LIBS technique, we studied the effect of applying static electric field with different polarities on the emission spectra obtained in a typical LIBS set-up. The effect of applying electric field on the plasma plume parameters, namely, plasma temperature Tp, and electron density ne has been studied. In addition to the spectroscopic analysis of the plasma plume, the plasma-induced shock waves was exploited to monitor the probable changes in the plasma plume dynamics, due to the applied electric field. Atomic and ionic spectral lines were affected differently due to the application of the electric field. However, the present study showed a pronounced enhancement in the signal to noise (S/N) ratio of different Al, neutral and ionized lines in case of longitudinal High Voltage (negative target and positive electrode). On the other hand there was a clear deterioration of the emission line intensities in case of reversed polarity. Such negative effect may be attributed to the suppression of the evolved plasma plume by the repulsive negative field. The plasma temperature tends to a constant value with the increasing electric field in both directions. This effect may be due the fact that the measured values of Tp are averaged for the whole plasma emission. The electron density decreases slightly in case of forward biasing, while the decrease is much stronger in case of reverse biasing. The slight decrease can be interpreted in view of the increase of the rate of electrons-ions recombination due to the presence of the electric field. On the other hand, positively biased target will attract a huge number of electrons from the plasma plume in the vicinity. The propagation velocity of the laser induced shock waves showed no significant changes under the effect of the applied electric field.