Abstract
State-of-the-art numerical simulations of quantum electrodynamical (QED) processes in strong laser fields rely on a semiclassical combination of classical equations of motion and QED rates, which are calculated in the locally constant field approximation. However, the latter approximation is unreliable if the amplitude of the fields, a 0, is comparable to unity. Furthermore, it cannot, by definition, capture interference effects that give rise to harmonic structure. Here we present an alternative numerical approach, which resolves these two issues by combining cycle-averaged equations of motion and QED rates calculated in the locally monochromatic approximation. We demonstrate that it significantly improves the accuracy of simulations of photon emission across the full range of photon energies and laser intensities, in plane-wave, chirped and focused background fields.
Highlights
The collision of multi-GeV electron beams and intense laser pulses is a promising scenario for precision measurements of quantum electrodynamics (QED) in the strong-field regime, where both the normalised amplitude of the laser, a0, and quantum nonlinearity parameter of the electron, χe, exceed unity
We describe how the locally monochromatic approximation (LMA) may be implemented in numerical simulations of photon emission and benchmark their predictions against strong-field QED for pulsed plane waves as well as with focusing pulses
We begin with an explanation of how the full QED plane-wave results are calculated, as well as a summary of the main details arising from the analytical calculation underpinning the LMA. (Many papers have investigated the effect of pulse shape on nonlinear Compton scattering, see e.g. [40, 48,49,50,51,52].) For concreteness, we specify from the outset that we will be assuming a background that is a circularly polarised, chirped, plane-wave pulse with potential A
Summary
The collision of multi-GeV electron beams and intense laser pulses is a promising scenario for precision measurements of quantum electrodynamics (QED) in the strong-field regime, where both the normalised amplitude of the laser, a0, and quantum nonlinearity parameter of the electron, χe, exceed unity. As yet, there are no experimental measurements charting the transition between the perturbative, multiphoton, and nonlinear regimes, 0.1 a0 10 at χe 1 This is likely to change in the near future, as increasing interest in strong-field QED has led to planned experiments that will combine conventional electron accelerators with intense optical lasers [12, 13]. We present a simulation framework that overcomes these issues by using the locally monochromatic approximation (LMA) instead This achieves greater accuracy by taking into account interference effects at the scale of the laser wavelength, which is possible provided that the laser pulse is relatively unchanged by the collision with a probe electron beam.
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