Time-resolved measurements of fast electron recirculation for relativistically intense femtosecond scale laser-plasma interactions

Green, J. S. and Booth, N. and Dance, R. J. and Gray, R. J. and MacLellan, D. A. and Marshall, A. and McKenna, P. and Murphy, C. D. and Ridgers, C. P. and Robinson, A. P. L. and Rusby, D. and Scott, R. H. H. and Wilson, L. (2019) Time-resolved measurements of fast electron recirculation for relativistically intense femtosecond scale laser-plasma interactions. Scientific Reports, 8 (1). 4525. ISSN 2045-2322 (https://doi.org/10.1038/s41598-018-22422-6)

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Abstract

A key issue in realising the development of a number of applications of high-intensity lasers is the dynamics of the fast electrons produced and how to diagnose them. We report on measurements of fast electron transport in aluminium targets in the ultra-intense, short-pulse (<50 fs) regime using a high resolution temporally and spatially resolved optical probe. The measurements show a rapidly (≈0.5c) expanding region of Ohmic heating at the rear of the target, driven by lateral transport of the fast electron population inside the target. Simulations demonstrate that a broad angular distribution of fast electrons on the order of 60° is required, in conjunction with extensive recirculation of the electron population, in order to drive such lateral transport. These results provide fundamental new insight into fast electron dynamics driven by ultra-short laser pulses, which is an important regime for the development of laser-based radiation and particle sources.

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