Determination of Stark Shifts and Widths Using Time Resolved Laser-Induced Breakdown Spectroscopy (LIBS) Measurements

Abstract

Stark broadening parameters have been estimated for resonant lines of Al(I) using time resolved measurements. The relation between the various emission line characteristics at different phases of opacity have been utilized to obtain the value of plasma temperature and Stark width parameters from the experimental data. The observed value of the center line intensity and Lorentzian component of the line width are compared against a simulated value of these parameters for optically thin case. The plasma temperature and Stark broadening parameters are obtained for the best fit condition by matching the experimentally observed and the simulated values of intensity and line widths. The time resolved measurements result in much better estimates for Stark parameters by allowing multiple points for fitting keeping the number of variables limited. The Stark shift parameters are also obtained from the slope of the plot of observed central wavelength shifts versus observed electron number density which is measured as a function of time. Hence, a method utilizing multiple-time observation data to obtain the Stark broadening parameters for lines showing self-absorption has been demonstrated.

Effect of laser energy on temporal evolution of self-absorption at different air pressures

“…This can be explained as follows: according to the ideal gas equation, the particle number densities of air at 10 −1 Pa and 10 −3 Pa are about 10 13 cm −3 and 10 11 cm −3 , respectively. These values are much lower than the electron density measured in experiment [26][27][28]. Therefore, when the air pressure is below 10 −1 Pa, the variation of air pressure has minimal impact on plasma.…”

“…This is because the laser energy in this experiment is sufficiently high, the laser energy density is 22.92 J cm −2 to 68.75 J cm −2 , and when the air pressure is 10 3 Pa, the radiation generated by plasma is intense, equivalent to that at 10 5 Pa. According to the ideal gas equation, the number density of air is about 10 15 cm −3 at an air pressure of 10 Pa, and it is about 10 11 cm −3 at 10 −3 Pa, which is much lower than the electron density observed in previous works [26][27][28]. Therefore, when the air pressure is below 10 Pa, the influence of ambient air on plasma is minimal, resulting in little or no significant change in spectral intensity of the target atom when the air pressure decreases.…”

Spatial confinement effects of laser-induced breakdown spectroscopy at reduced air pressures

“…5, the Stark shifts of the line gradually decreased with the increasing delay times. This was because the stark shifts of the spectral line were proportional to the electron number density, based on the following equation [37]: where d s is Stark shift parameter, and n e (cm −3 ) is the number density of electrons in the plasma. The n e decreased with the increasing delay times, and the Stark shifts was also reduced accordingly.…”

Atomic spectrometry update: review of advances in atomic spectrometry and related techniques

“…The two other papers by the same authors dealt separately with Stark broadening of 18 Mo I and 18 Mo II lines 68 and 43 Mo II lines 69 under similar conditions of n e ≈ 1.5 × 10 23 m −3 and T e ≈ 13 000 K. It should be noted the three studies also included an Abel inversion to account for radial inhomogeneity. In contrast, Kumar et al 70 determined Stark widths of Al I lines in a LIBS plasma using a different method of calculation to estimate self-absorption. They utilised experimental values of the line width and peak intensity, obtained from time resolved LIBS measurements, which were fitted with calculated values for the optically thin case.…”