Diagnostics of laser-produced Mg plasma through a detailed collisional radiative model with reliable electron impact fine structure excitation cross-sections and self-absorption intensity correction

Abstract

A detailed fine-structure resolved collisional radiative model is developed to investigate the laser-produced Mg plasma. The dominant processes linked with the electron impact excitation and de-excitation have been considered explicitly in a very reliable and consistent manner in the present model. The required electron impact excitation cross-sections of Mg for the large number of transitions from the ground state 3s2 (J = 0) to the 3s3p, 3s4s, 3s3d, 3s4p, 3s5s, 3s4d, 3s5p, 3s6s, 3s5d, and 3s6p excited states and from 3s3p manifolds to the other fine-structure levels of 3s4s, 3s3d, 3s5s, 3s4d, 3s6s, and 3s5d configurations are obtained using the fully relativistic distorted wave approach. To ensure the accuracy of our calculations, where available, the oscillator strengths and cross-sections are compared with previous measurements and other calculations. Further, plasma diagnostics are carried out by coupling the present collisional radiative model with the laser-induced breakdown spectroscopy measurements reported by Delserieys et al (2009 J. Appl. Phys., 106, 083304). Five measured intense emission lines of Mg viz 383.3, 470.3, 517.8, 552.8, and 571.1 nm are used and corrected through the self-absorption to extract the plasma parameters i.e. electron temperature and electron density. The obtained plasma parameters at different delay times ranging from 100–700 ns are compared with the results of Delserieys et al (2009 J. Appl. Phys., 106, 083304) that were estimated using the Thomson scattering and Boltzmann plot approaches.

Electron impact cross-sections and rate coefficients of Si+2 ions relevant to collisional radiative modeling of silicon plasma

“…The higher cross-section for this transition is due to being a resonance transition, as expected. It is an established fact that the first dipole allowed 1 P 1 excitation cross-section of the two electron systems are always found to be the highest as compared to other transitions [26]. However, our calculated transition probability for this transition is 3.36 × 10 9 s −1 which is the highest as compared to the values for other transitions and similar can be seen from the values available in the NIST database [38].…”

“…We have calculated the electron impact cross-sections using relativistic distorted wave (RDW) theory [28] which has been found to be very useful to calculate cross-sections at intermediate and high energy of the projectile electron. We have also shown in our previous work on electron excitations of Ne [29] and Mg [26] that the RDW cross-sections are in good agreement, even in the near threshold low electron energy region, with the experimental results [30,31] and the other theoretical calculations like R-matrix/CCC [32,33] which have been considered specifically reliable in such an energy region. Our group has earlier reported on the cross-sections for various atoms/ions using RDW theory and found good agreement with available measured and theoretical data [28,29,34].…”

“…Therefore, to properly take into account the nonequilibrium nature of the plasma, OES measurements are required to couple with suitable population kinetic models [13]. The CR modeling [26] is a very comprehensive population kinetic modeling technique in which all the dominant populating and depopulating collisional and radiative processes occurring inside the plasma viz., electron impact excitation (EIE) and de-excitation, ionization, quenching, diffusion, radiative decay, recombination, self-absorption, etc are required to be considered and the population balance equation are solved simultaneously for different energy levels of any emitting specie to obtain the line emission intensities for different sets of plasma parameters (n e , T e ). These calculated line emission intensities can then be matched with the corresponding OESmeasured intensities to obtain the parameters of the plasma.…”

Non-invasive optical characterization and estimation of Zn porosity in gas tungsten arc welding of Fe–Al joints using CR model and OES measurements

“…The electron impact cross-sections are used from previous calculations using a fully relativistic distorted wave (RDW) approximation. The RDW cross-sections are consistent and in good agreement with previously reported values for the relevant transitions and employed successfully in various plasma modeling and diagnostic applications [21][22][23][24]. It is worth noting that to develop CR models, one needs cross sections for a significantly large number of transitions in a wide projectile energy range.…”

“…Here 'f' and 'm' represent the upper energy level while 'i' and 'n' represent the lower energy level of the respective transition. In the present work, Zn-I 468 nm line is chosen as a reference line [22,26].…”