Laser, optical and electrical diagnostics of colliding laser-produced plasmas

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

Emission characteristics and dynamics of the stagnation layer in colliding laser produced plasmas

The expansion dynamics of ion and neutral species in laterally colliding laser produced aluminum plasmas have been investigated using time and space resolved optical emission spectroscopies and spectrally and angularly resolved fast imaging. The emission results highlight a difference in neutral atom and ion distributions in the stagnation layer where, at a time delay of 80 ns, the neutral atoms are localized in the vicinity of the target surface 1 mm from the target surface while singly and doubly charged ions lie predominantly at larger distances, 1.5 and 2 mm, respectively. The imaging results show that the ions were found to form a well defined, but compressed, stagnation layer at the collision front between the two seed plasmas at early times (Dt ~ 80 ns). On the other hand, the excited neutrals were observed to form a V-shaped emission feature at the outer regions of the collision front with enhanced neutral emission in the less dense, cooler regions of the stagnation layer

Emission characteristics and dynamics of the stagnation layer in colliding laser produced plasmas

The expansion dynamics of ion and neutral species in laterally colliding laser produced aluminium plasmas have been investigated using time and space resolved optical emission spectroscopy and spectrally and angularly resolved fast imaging. The emission results highlight a difference in neutral atom and ion distributions in the stagnation layer where, at a time delay of 80 ns, the neutral atoms are localised in the vicinity of the target surface (< 1 mm from the target surface) while singly and doubly charged ions lie predominantly at larger distances, < 1.5 mm and < 2 mm respectively. The imaging results show that the ions were found to form a well defined, but compressed, stagnation layer at the collision front between the two seed plasmas at early times (Δt < 80 ns). On the other hand the excited neutrals were observed to form a V shaped emission feature at the outer regions of the collision front with enhanced neutral emission in the less dense, cooler regions of the stagnation layer.Science Foundation IrelandHigher Education AuthorityIrish Research Council for Science, Engineering and Technologyab, li - TS 28.03.1

Emission characteristics and dynamics of the stagnation layer in colliding laser produced plasmas

The expansion dynamics of ion and neutral species in laterally colliding laser produced aluminium plasmas have been investigated using time and space resolved optical emission spectroscopy and spectrally and angularly resolved fast imaging. The emission results highlight a difference in neutral atom and ion distributions in the stagnation layer where, at a time delay of 80 ns, the neutral atoms are localised in the vicinity of the target surface (< 1 mm from the target surface) while singly and doubly charged ions lie predominantly at larger distances, < 1.5 mm and < 2 mm respectively. The imaging results show that the ions were found to form a well defined, but compressed, stagnation layer at the collision front between the two seed plasmas at early times (Δt < 80 ns). On the other hand the excited neutrals were observed to form a V shaped emission feature at the outer regions of the collision front with enhanced neutral emission in the less dense, cooler regions of the stagnation layer.Science Foundation IrelandHigher Education AuthorityIrish Research Council for Science, Engineering and Technologyab, li - TS 28.03.1

Electron and ion stagnation at the collision front between two laser produced plasmas

We report results from a combined optical interferometric and spectrally resolved imaging study on colliding laser produced aluminium plasmas. A Nomarski interferometer was used to probe the spatio-temporal distribution of the electron density at the collision front. Analysis of the resulting interferograms reveals the formation and evolution of a localised electron density feature with a well defined profile reminiscent of a stagnation layer. First signs of electron stagnation are observed at a time delay of 10 ns after the peak of the plasma generating laser pulse. The peak electron density was found to exceed 1019 cm−3 and the layer remained well defined up to a time delay of ca. 100 ns. Temporally and spectrally resolved optical imaging was also undertaken to compare the Al+ ion distribution, with that of the 2D electron density profile. This revealed nascent stagnation of singly charged ions at a delay time of 20 ns. We attribute these results to the effects of space charge separation in the seed plasma plumes.Science Foundation IrelandHigher Education AuthorityIrish Research Council for Science, Engineering and Technologyti, ke, ab, st, en, li - TS 27.03.1