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Experimental Investigations of Carbon and Titanium Molecular Species in Laser Ablation Plumes
AuthorIratcabal, Jeremy J.
AdvisorCovington, Aaron M.
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A new multi-parameter apparatus has been developed for this dissertation in order to study laser ablation. The purpose of this apparatus is to better understand the evolution and energy partitioning of an ablation plume from the warm dense plasma stage to the cool neutral gas stage. The Laser Ablation Plume Experiment (LAPeX) apparatus was designed and built to include a large number of optical and spectroscopic diagnostics, various background environment configurations, and adjustable laser intensity. This new experimental platform required the design, assembly, alignment, calibration, and testing of the various components involved. Extensive metrology and characterization of the diagnostic elements of the apparatus were undertaken to ensure the quality of the data. Diatomic carbon was investigated using absorption spectroscopy. Graphite was ablated into a 100 Torr nitrogen atmosphere with a 1,024 nm pulsed Nd:YAG laser. A quasi-CW supercontinuum laser was used to generate the absorption probe beam. High resolution spectroscopic data of the Swan bands for Δv = 0 and Δv = 1 was collected and compared to simulations. A data reduction method was developed to extract an absorption spectrum from the data. Simulations indicated that the plume was not in thermodynamic equilibrium. TiO was produced by ablating titanium into a 100 Torr oxygen atmosphere. TiO absorption is observed in material ejected from the yellow hypergiant ρ Cassiopeiae. Fast imaging of the plume, with a band-pass filter to allow only TiO γ band emission, showed emission at t ≥ 5 μs after target irradiation. Spectroscopic analysis of emission from neutral titanium at 5 μs indicated a temperature of ∼1,000 K. The strongest TiO emission was observed 1-3 mm behind the shock wave with fast imaging and spectroscopy.