Laser opacity in underdense preplasma of solid targets due to quantum electrodynamics effects

Wang, W. M. and Gibbon, P. and Sheng, Z. M. and Li, Y. T. and Zhang, J. (2017) Laser opacity in underdense preplasma of solid targets due to quantum electrodynamics effects. Physical Review E, 96 (1). ISSN 2470-0045

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    Abstract

    We investigate how next-generation laser pulses at 10-200PW interact with a solid target in the presence of a relativistically underdense preplasma produced by amplified spontaneous emission (ASE). Laser hole boring and relativistic transparency are strongly restrained due to the generation of electron-positron pairs and γ-ray photons via quantum electrodynamics (QED) processes. A pair plasma with a density above the initial preplasma density is formed, counteracting the electron-free channel produced by hole boring. This pair-dominated plasma can block laser transport and trigger an avalanchelike QED cascade, efficiently transferring the laser energy to the photons. This renders a 1-μm scale-length, underdense preplasma completely opaque to laser pulses at this power level. The QED-induced opacity therefore sets much higher contrast requirements for such a pulse in solid-target experiments than expected by classical plasma physics. Our simulations show, for example, that proton acceleration from the rear of a solid with a preplasma would be strongly impaired.