Simplified plasma model for the heuristic approach. (a) The plasma is described by two shells: an inner sphere or plasma core S1 and an outer shell S2. The ambient atmosphere is described by shell S3; (b) densities and (c) temperature distribution in the regions S1–S3.
Side-on high-speed images of the laser-induced plasma on an iron sample for (a) a single pulse of 80 mJ, (b) a symmetric collinear double pulse with , and (c) an unsymmetric collinear double pulse with and . The numbers in the upper right corner of each image show the delay time in microseconds of the start of the exposure with respect to the last pulse irradiated. The exposure time itself of each frame was kept constant and amounts to 50 ns. The further measuring parameters are and . The laser is irradiated from the top; the black horizontal line marks the position of the sample surface.
Schematic illustration of the heuristic model to calculate the spectral plasma emission.
Shell model of the plasma and integration paths of the radiation transport equation.
Measured iron spectrum (solid line, measurement parameters: see text) and calculated spectrum (dotted line) using the following values: , , , and ; , , , and ; , , and . For the lines marked with an “S,” Stark width broadening parameters are published.
Al I line at 394.4 nm with line reversal. Top: experimental spectrum (solid line) and Lorentz fit curve to the wings (dash-dot line). Bottom: experimental spectrum and calculated line profile (dotted line) using the following values: , , , and ; , , , and ; , , and .
Simulated emission spectra in the VUV range for a steel sample with emission lines of carbon, phosphorus, and sulfur. Top: no absorption in the ambient atmosphere, middle/bottom: 0.1% and 0.2% oxygen content.
List of input quantities and their description for the heuristic model.
List of Fe I lines in the spectral range shown in Fig. 6 belonging to multiplets where Stark broadening data are partially available. The Stark width broadening constant shown in the third column is the average of the ratios of the Stark width and the electron density measured for different temperatures for a given line taken from Ref. 24. The Stark shift refers to an electron density of . Only those data of Ref. 24 were taken, where an uncertainty classification of grade A, , or B is stated corresponding to uncertainties being within 15%, 23%, and 30%.
Stark data of the Al I line 394.401 nm published for different electron densities and temperatures. Only those values marked with “*” having accuracies between 30% and 50% are taken to calculate an average Stark width broadening constant to be used for the simulation: . For the shift, the value is taken for the simulation.
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