Micron-scale mapping of megagauss magnetic fields using optical polarimetry to probe hot electron transport in petawatt-class laser-solid interactions

Chatterjee, Gourab and Singh, Prashant Kumar and Robinson, A. P.L. and Blackman, D. and Booth, N. and Culfa, O. and Dance, R. J. and Gizzi, L. A. and Gray, R. J. and Green, J. S. and Koester, P. and Kumar, G. Ravindra and Labate, L. and Lad, Amit D. and Lancaster, K. L. and Pasley, J. and Woolsey, N. C. and Rajeev, P. P. (2017) Micron-scale mapping of megagauss magnetic fields using optical polarimetry to probe hot electron transport in petawatt-class laser-solid interactions. Scientific Reports, 7 (1). 8347. ISSN 2045-2322 (https://doi.org/10.1038/s41598-017-08619-1)

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Abstract

The transport of hot, relativistic electrons produced by the interaction of an intense petawatt laser pulse with a solid has garnered interest due to its potential application in the development of innovative x-ray sources and ion-acceleration schemes. We report on spatially and temporally resolved measurements of megagauss magnetic fields at the rear of a 50-μm thick plastic target, irradiated by a multi-picosecond petawatt laser pulse at an incident intensity of ~1020 W/cm2. The pump-probe polarimetric measurements with micron-scale spatial resolution reveal the dynamics of the magnetic fields generated by the hot electron distribution at the target rear. An annular magnetic field profile was observed ~5 ps after the interaction, indicating a relatively smooth hot electron distribution at the rear-side of the plastic target. This is contrary to previous time-integrated measurements, which infer that such targets will produce highly structured hot electron transport. We measured large-scale filamentation of the hot electron distribution at the target rear only at later time-scales of ~10 ps, resulting in a commensurate large-scale filamentation of the magnetic field profile. Three-dimensional hybrid simulations corroborate our experimental observations and demonstrate a beam-like hot electron transport at initial time-scales that may be attributed to the local resistivity profile at the target rear.

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