Abstract
Strong-field quantum electrodynamics predicts electron-seeded electron–positron pair cascades when the electric field in the rest-frame of the seed electron approaches the Sauter–Schwinger field, i.e. . Electrons in the focus of next generation multi-PW lasers are expected to reach this threshold. We identify three distinct cascading regimes in the interaction of counter-propagating, circularly-polarised laser pulses with a thin foil by performing a comprehensive scan over the laser intensity (from 1023 to 5 × 1024 W cm−2) and initial foil target density (from 1026 to 1031 m−3). For low densities and intensities the number of pairs grows exponentially. If the intensity and target density are high enough the number density of created pairs reaches the relativistically-corrected critical density, the pair plasma efficiently absorbs the laser energy (through radiation reaction) and the cascade saturates. If the initial density is too high, such that the initial target is overdense, the cascade is suppressed by the skin effect. We derive a semi-analytical model which predicts that dense pair plasmas are endemic features of these interactions for intensities above 1024 W cm−2 provided the target’s relativistic skin-depth is longer than the laser wavelength. Further, it shows that pair production is maximised in near-critical-density targets, providing a guide for near-term experiments.
Highlights
To correctly describe the interaction of strong electromagnetic fields with matter requires strong-field quantum electrodynamics (QED)
The experimental realisation of laser-induced cascades will mark the transition to a regime, as yet only inferred in astrophysical environments, where strongfield QED and plasma effects are coupled [12, 13]. This is in contrast to experiments where nonlinear Compton scattering [27,28,29,30] and multi-photon Breit–Wheeler pair production [31] have previously been observed in the interaction of electron beams with intense lasers, i.e. not in a plasma environment
We showed in figure 1 that as the initial target density decreases below the relativistically-corrected critical density the temporal evolution of the number of pairs looks similar but is shifted to later time as the cascade must grow from fewer particles and the growth rate per particle is the same
Summary
Strong-field quantum electrodynamics predicts electron-seeded electron–positron pair cascades. If the intensity and target density are high enough the number density of created pairs reaches the relativistically-corrected critical density, the pair plasma efficiently absorbs the laser energy (through radiation reaction) and the cascade saturates. We derive a semi-analytical model which predicts that dense pair plasmas are endemic features of these interactions for intensities above 1024 W cm−2 provided the target’s relativistic skin-depth is longer than the laser wavelength. It shows that pair production is maximised in near-critical-density targets, providing a guide for near-term experiments
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