Spectroscopic modeling and characterization of a laser-ablated lithium-silver plasma plume

In this dissertation, the modeling and spectroscopic analysis of optical line emission recorded during the laser ablation of plasma plumes from a solid Li-Ag alloy target is discussed. The spectral model considers the effects of multi-element collisional-radiative atomic kinetics, detailed Stark-broadened line profiles, and radiation transport. To compute the atomic data of neutrals and low-charge ions a semi-empirical procedure was implemented in a Hartree-Fock atomic structure code, that produces a set of wavefunctions consistent with measured energy levels. This procedure is critical to obtain spectroscopic quality atomic data for a transition element like silver. A large database of atomic cross sections and rates was computed to input the atomic kinetics calculations. Detailed line shapes were calculated for the Li and Ag line transitions observed in the experimental spectra taking into account the effects of natural, Doppler, Stark and resonance broadening. The radiation transport equation was solved to calculate the transport of the lines through the plasma and the emitted line intensity distribution. The final synthetic spectra self-consistently includes the Li and Ag line emissions. The temperature and density sensitivity of these spectra is discussed for the case of uniform and non-uniform plasmas.; The spectral model was implemented in a versatile and efficient parallel processing code, and applied to the analysis of data recorded in laser ablation experiments performed at Sandia National Laboratories. First, raw data images recorded with a gated, space-resolving spectrograph were corrected for instrument efficiency, and the wavelength and space axes calibrated. Then, a collection of time- and space-resolved spectra lineouts was extracted for analysis. The results of the analysis indicate that early in time and close to the target's surface a dense plasma is formed with electron temperatures in the 1 eV to 2 eV range, and electron densities in the 1 × 1017 cm −3 to 1 × 1018 cm−3. The impact of plasma non-uniformities and opacity on the formation of the spectra close to the surface is discussed. Late in time and away from the surface the spectra are characteristic of a plasma undergoing a time-dependent (i.e. non-steady-state) recombination driven by thermal cooling and fast expansion. These results are important for testing hydrodynamic models of laser ablation and understanding the dynamics of plasma plumes.