A fine-structure-resolved collisional radiative model for Ti plasma

This study develops a fine-structure-resolved collisional-radiative model to analyze laser-produced titanium (Ti) plasma. The required electron impact excitation cross-sections are computed for transitions from the lowest 22 fine structure states arising from ground 3d24s2 and first excited 3d34s configurations to higher fine-structure levels using the fully relativistic distorted wave method. Atomic structure calculations are performed using the multi-configuration Dirac-Hartree-Fock approach, and the resulting transition probabilities are validated against data from the NIST database. The model incorporates key atomic processes, including radiative decay, electron impact excitation and de-excitation, electron impact ionization, and three-body recombination. For plasma diagnostics, we integrate our collisional-radiative model with laser-induced breakdown spectroscopy data from Mejia et al. (IEEE Transactions on Plasma Science, 51(10), 2023, 3035–3052). Eight Ti emission lines observed at a plasma delay of 3.5 μs are used to analyze the experimentally measured Ti plasma produced at a laser energy of 48 mJ. The extracted electron temperature and electron density are compared with values obtained from the experimental study.