Diagnostics of laser-produced Ba plasma using a detailed collisional-radiative model and extensive electron impact excitation cross-sections

Abstract We developed a fine-structure-resolved collisional-radiative (CR) model for diagnostics of laser-produced Ba plasma. In such plasmas, electron impact excitation (EIE) processes are dominant however, their cross-sections are not sufficiently available in the literature to develop a suitable CR model. To address this gap, we first calculated EIE cross-sections using the relativistic distorted wave method for transitions from the ground state (6 s 2 1 S 0 ) and seven metastable states (6s5d 3 D <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>1</mml:mn> <mml:mo>,</mml:mo> <mml:mn>2</mml:mn> <mml:mo>,</mml:mo> <mml:mn>3</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> , <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msup> <mml:mrow/> <mml:mn>1</mml:mn> </mml:msup> <mml:msub> <mml:mi>D</mml:mi> <mml:mn>2</mml:mn> </mml:msub> </mml:mrow> </mml:math> ; 6s6p 3 P <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mrow/> <mml:mrow> <mml:mn>0</mml:mn> <mml:mo>,</mml:mo> <mml:mn>1</mml:mn> <mml:mo>,</mml:mo> <mml:mn>2</mml:mn> </mml:mrow> </mml:msub> </mml:mrow> </mml:math> ) to various excited fine-structure levels. The required atomic structure calculations were performed using the multi-configuration Dirac-Fock (MCDF) method, with excitation energies validated against available data, showing strong agreement. The calculated EIE cross-sections, along with the inclusion of other collisional and radiative processes such as electron de-excitation, ionization, three-body recombination, and radiative decay, were incorporated into the CR model. The rate balance equations were formulated and solved over an anticipated range of electron temperatures ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>T</mml:mi> <mml:mtext>e</mml:mtext> </mml:msub> </mml:mrow> </mml:math> ) and densities ( <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mrow> <mml:msub> <mml:mi>n</mml:mi> <mml:mtext>e</mml:mtext> </mml:msub> </mml:mrow> </mml:math> ) to determine the population densities of fine-structure levels. Using these, the line intensities of selected transitions were obtained. The model was validated using experimental spectroscopic measurements from Singh et al (2015 Appl. Opt. 54 7673), covering six prominent emission lines (408–553 nm), with self-absorption effects corrected using the internal reference self-absorption correction method. A detailed comparison of normalized intensities obtained from our CR model and experimentally reported values was carried out, demonstrating strong agreement and enabling the extraction of accurate plasma parameters. This work establishes a robust CR model, incorporating detailed atomic processes and reliable EIE cross-sections, providing a validated framework for diagnosing laser-produced Ba plasma.