Avalanche Ionization Revisited: Ultrafast Plasma Dynamics and Applications

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This project will investigate the phenomenon of avalanche ionization. One of the earliest and most impressive feats of the laser, soon after it was invented, was the demonstration that focusing laser pulses with a lens into air could generate a loud and very bright ‘breakdown spark’, in which the molecules were broken up and ionized, with the air strongly heated to temperatures approaching that of the Sun. While this result has stimulated much theory and modeling work over the decades and underlies several important technologies, detailed experimental investigation of the onset of this "avalanche" process has never been done -- mainly because the advanced laser-based diagnostic tools that would enable such an investigation were not available until recently.Breakdown sparks proceed by avalanche ionization, in which a single seed electron is multiplied exponentially into a strongly heated cloud by a driving laser field. The experiments of this program will use the latest Univ. of Maryland-developed high resolution diagnostics to investigate the detailed time and space development of the avalanche proceeding from a single electron, and the interaction of the rapidly growing hot plasma cloud with the surrounding gas. In addition, avalanche breakdown will be investigated as an ultrasensitive detection technique for trace species.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.