We report on investigations of plasmas produced by laser ablation of fresh potatoes using infrared nanosecond laser radiation. A twin laser system consisting of two Nd:YAG oscillators was used to generate single or double pulses of adjustable interpulse delay. The potatoes were irradiated under ambient air with moderate pulse energies of about 10 mJ. The expansion dynamics of the ablation plume was characterized using fast imaging with a gated camera. In addition, time-resolved optical emission spectroscopy was applied to study the spectral line emission of the various plasma species. The electron density was deduced from Stark broadening, and the plasma temperature was inferred from the relative emission intensities of spectral lines. The relative concentrations of metals were estimated from the comparison of the measured emission spectra to the spectral radiance computed for a plasma in local thermal equilibrium. It is shown that the plasma produced by double pulses has a larger volume and a lower density. These properties lead to an increase of the signal-to-noise ratio by a factor of 2 and thus to an improved measurement sensitivity.
Laser-induced breakdown spectroscopy (LIBS) is a technique that can provide qualitative and quantitative measurements of the сharacteristics of irradiated metals. In the present work, we have calculated the parameters of the plasma produced from a brass alloy sample under the action of a pulsed Nd : YAG laser operating at 1064 nm. The emission lines of copper atoms (Cu I), zinc atoms (Zn I), and lead atoms (Pb I), which are elements of a brass alloy composition, were used to investigate the parameters of the brass plasma. The spectral profiles of Cu, Zn, and Pb lines have been used to extract the electron temperature and density of the brass alloy plasma. The characteristics of Cu, Zn, and Pb were determined quantatively by the calibration-free LIBS (CF-LIBS) method considering for accurate analysis that the laser-induced ablated plasma is optically thin in local thermodynamic equilibrium conditions and the plasma ablation is stoichiometric. The Boltzmann plot method was used to evaluate the plasma temperature, and the Stark broadened profiles were used to determine the electron density. An algorithm based on the experimentally measured values of the intensity of spectral lines and the basic laws of plasma physics was developed for the determination of Cu, Zn, and Pb concentrations in the brass sample. The concentrations calculated by CF-LIBS and the certified concentrations were very close.
Theoretical studies of a phototriggered XeCl excimer laser have been performed through the development of a zero-dimensional model and used for conditions close to experiment for about 50–100 ns laser pulse duration with electron power deposition in the MW/cm3 range and inside a 300 cm3 chamber. The well-known parallel resistor network model is used. The plasma generated by the impulse discharge is represented by one or more resistance in parallel, whose conductivity is proportional to the electron density. Time variation of the electron density is obtained by integrating the transport equations coupled to the heavy species kinetic and the external circuit. This study provides the time variation of the discharge characteristics as well as the influence of the gas composition on these characteristics. The results have been discussed and analyzed. Calculated discharge current and voltage are also compared with experimental results. Finally, the use of the present model allows a good comprehension of the halogen depletion phenomena, which is the principal cause of laser ending and allows a simple study of the evolution of a large-scale heterogeneity in preionization density and its effect on electrical and chemical plasma properties.
A global one-dimensional model of a dielectric barrier discharge which includes the sheath region and the positive column was developed. The model was used to study the electrical properties under operating conditions of the vacuum ultraviolet excimer lamp and to understand the basic processes of plasma kinetics. A 0.5cm interelectrode gap distance is filled with a Ne-Xe-HCl mixture. Time variations of the charged particles and excited species in the positive column were described. Then the one-dimensional model was used in the cathode region to illustrate (i) the spatio-temporal behavior of electronic and ionic densities and the electric field, and (ii) the time variation of the voltage, the current, and secondary currents due to ion and photon (λ=172nm) impact on the cathode. It shows a good resolution inside the sheath at high pressure and it correctly predicts the waveform of the discharge behavior. The obtained results have been discussed and analyzed.
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