Time and spatially resolved laser induced ablation plumes

Laser ablation is the process of removing material from a solid or liquid surface by irradiating it with a laser beam. Typically this is done with a pulsed laser in which the energy is deposited in a small volume (skin depth region) in the target which results in melting and evaporation for low (less then 108 W/cm2) pulse intensities. It is the goal of this thesis to outline an approach to and experimental work done on describing how the initial laser pulse energy is distributed between a solid graphite target and the resulting ablation plume. Chapter one gives an introduction of the research motivation on this topic developed and evolved and some theoretical discussion on laser ablation. The second chapter describes the experimental apparatus built for laser-graphite interaction experiments using a Nd:YAG 5ns pulsed laser system impinging on a target in air, He and vacuum. Each major component of the apparatus is discussed. Chapter three gives a detailed description of experimental techniques used and our method of acquiring and storing data. Next, a chapter covering many of our results is given. We have observed and measured viable light spectra and images of plumes formed in the interaction. Also, we observed vortex stabilized structures with lifetimes up to 100mus in air and spectroscopically we observed the plume to be dominated by C2. Lastly, chapter five is a concluding chapter summarizing our work, in which we use the results presented in chapter four to put limits on the distribution of the laser pulse energy into the solid target and ablation plume.