Electron and ion stagnation at the collision front between two laser produced plasmas
Hough, Pádraig and McLoughlin, Conor and Kelly, Thomas J. and Hayden, Patrick and Harilal, Sivanandan S. and Mosnier, Jean-Paul and Costello, John T. (2009) Electron and ion stagnation at the collision front between two laser produced plasmas. Journal of Physics D: Applied Physics, 42 (5).
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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 electron densities at the collision front. Analysis of the resulting interferograms reveals the formation and evolution of a localized electron density feature with a well-defined profile reminiscent of a stagnation layer. Electron stagnation begins at a time delay of 10 ns after the peak of the plasma generating laser pulse. The peak electron density was found to exceed 10^19 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.
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