Spectroscopic Imaging of Aluminum Containing Plasma

This dissertation aims to characterize laser-induced plasma from a physics point of view as warm, dense matter. Use of nominal nanosecond pulsed laser radiation initiates a plasma with electron temperatures of the order of 10 electron volts and electron densities of the order of air species densities at standard ambient temperature and pressure. For laser ablation and/or optical breakdown at or near a solid surface, the electron density can amount to be 1000 times greater. Spectroscopic investigations of the plasma emissions provide a method by which the electron density, temperature, and shockwave expansion may be determined. Of particular interest are the earliest of times following ablation of an aluminum target sample. At these times, observed spectral line profiles become distorted due to self-absorption affects. Here, experimental corrections to self-absorbed Al 394.4 and 396.15 nm, ground state transitions and the hydrogen Balmer series alpha, beta, and gamma lines are calculated by retro-reflecting the plasma emission back through the plasma volume. The plasma are initiated by laser ablating an Al alloy 6061 target sample in a 90 percent hydrogen and 10 percent nitrogen gas atmosphere at 840 Torr with 1064 nm Nd:YAG 14 ns laser pulses. Electron densities are calculated by fitting the corrected profiles to Voigt profiles. The widths of the lines are used with empirically developed formulas to infer the electron density. The temperature of the plasma is found by using the Boltzmann plot method constructed from the Balmer series lines. Spatially resolved, diatomic molecular aluminum monoxide spectra are fit to theory spectra to infer the plasma temperature along the axis of the laser incidence at time delays greater than 2.5 microseconds following target ablation. Computer tomography methods, including Abel inversion, are used to find the radial profile of the inferred temperatures. Finally, a series of measurements of the plasma shockwave are presented to determine the geometry of the shock front expansion using the shadowgraph imaging technique.