Laser, optical and electrical diagnostics of colliding laser-produced plasmas
Hough, Pádraig (2010) Laser, optical and electrical diagnostics of colliding laser-produced plasmas. PhD thesis, Dublin City University.
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This thesis describes the development of and results from a new laboratory facility designed to investigate the properties and explore potential applications of
colliding laser produced plasmas.
When two plasmas collide there are two extreme scenarios that can play out – the plumes can either interpenetrate or stagnate depending on the ion-ion mean free path. During interpenetration, the plasmas stream through each other, the main interaction amounting to binary collisions. In the case of stagnation, rapid accumulation of plasma material at the collision front leads to the formation of a dense
layer of material between the two plasmas.
Interferometry of single laser produced plasmas created in background gaseous atmospheres expose the presence of a shock front at the plasma gas interface which rapidly expands outwards. Shadowgraphy is currently the most widely employed diagnostic technique to analyse such shock fronts and a comparison of both techniques reveals that interferometry can be used to diagnose the interaction of laser produced plasmas in gaseous environments in pressure regimes where other techniques such as shadowgraphy are not sensitive.
Optical diagnostics such as laser interferometry, fast imaging (angularly resolved) and optical emission spectroscopy have been employed to probe colliding
plasmas, revealing important factors in the formation of the stagnation layer. For example the studies have found that electrons stagnate before ions and similarly ions
stagnate before neutral species.
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