Modeling of laser produced Zn plasma with detailed electron impact fine structure excitation cross-sections

Abstract

An intricate collisional radiative (CR) model is developed including all the important processes for the laser induced zinc plasma. The electron impact excitation (EIE) and de-excitation of several fine structure levels of Zn play a dominant role in the laser induced plasma and their cross-sections are needed. In view of this, an extensive calculation is performed to obtain the EIE cross-sections of the large number of fine structure transitions of zinc atom. The cross-sections of Zn are calculated and presented for the excitations from its ground state 4s2 (J = 0) as well as from the 4s4p excited state to the various fine structure levels of different excited states using fully relativistic distorted wave (RDW) theory. In the calculation, relativistic multi-configuration bound target atomic wave functions are obtained through GRASP2K program using 4s2, 4s4p, 4s5s, 4s5p, 4s4d, 4s6s, 4s6p, 4s5d, 4s7s and 4s7p configuration state functions while the projectile incident and scattered electron distorted wave functions are obtained by solving the relativistic Dirac equations. Further, the calculated cross-sections are incorporated in the CR model for the plasma characterization as the various rate coefficients are linked through their corresponding cross-sections. The model gives the state population distribution of the fine structure energy levels of the neutral Zn atom considered in the model and from which the intensities of the line emissions are obtained. The calculated intensities from the CR model for the four emission lines (334.5, 468, 472, and 481 nm) are matched with the spectroscopic measurements (Smijesh et al 2013 J. Appl. Phys. 114 093301) and the plasma parameters viz electron density and electron temperature are evaluated. The plasma parameters are presented at different ambient pressures in the range of 0.05–10 Torr.