Evaluation of pressure in a plasma produced by laser ablation of steel

Abstract

We investigated the time evolution of pressure in the plume generated by laser ablation with ultraviolet nanosecond laser pulses in a near-atmospheric argon atmosphere. These conditions were previously identified to produce a plasma of properties that facilitate accurate spectroscopic diagnostics. Using steel as sample material, the present investigations benefit from the large number of reliable spectroscopic data available for iron. Recording time-resolved emission spectra with an echelle spectrometer, we were able to perform accurate measurements of electron density and temperature over a time interval from 200 ns to 12 µs. Assuming local thermodynamic equilibrium, we computed the plasma composition within the ablated vapor material and the corresponding kinetic pressure. The time evolution of plume pressure is shown to reach a minimum value below the pressure of the background gas. This indicates that the process of vapor-gas interdiffusion has a negligible influence on the plume expansion dynamics in the considered timescale. Moreover, the results promote the plasma pressure as a control parameter in calibration-free laser-induced breakdown spectroscopy.

Shock Waves in Laser-Induced Plasmas

“…Other important computational and experimental studies on laser-induced shock waves were performed by Harilal and coworkers [12][13][14], in the framework of extensive and articulated research devoted to the study of the expansion of the laser plume in different ambient gases and experimental configurations [15][16][17][18][19][20]. In a recent paper, Hermann et al [21] studied the Figure 3. Expansion of the spherical shock wave produced by a Nd:YAG laser in gas (black points: Air at pressure of 760 torr; red points: Nitrogen at 760 torr; and blue points: He at 2100 torr).…”

Local thermodynamic equilibrium in a laser-induced plasma evidenced by blackbody radiation

“…According to their large initial density, the processes of relaxation are faster whereas the diffusion processes are slower [7,8]. Due to the high initial pressure, the ablated material plume expands rapidly until it reaches a pressure equilibrium with the surrounding gas atmosphere [9,10]. It was shown that for laser irradiation with ultraviolet nanosecond laser pulses, the plasma appears almost uniform if ablation occurs under an inert gas atmosphere [11].…”

Two-step procedure for trace element analysis in food via calibration-free laser-induced breakdown spectroscopy

“…The temperoral evolution was approximated by functions f (t) = At B represented by the continuous lines. This approximation was shown to describe closely the variations n e (t) and T (t) in plasmas produced by laser ablation of different materials under indentical irradiation conditions [32,40,24]. (0,0) Figure 9: Molecular bands and atomic transitions emitted from major and most abundant minor elements.…”

“…The atmospheric pressure is here an arbitrary choice that corresponds to a time between the early and late measurements [40]. According to the strong dependence of the chemical equilibrium on temperature and the weaker dependence on pressure, the temperature-dependence of plasma species shown in Fig.…”