Abstract
The recoil associated with photon emission is key to the dynamics of ultrarelativistic electrons in strong electromagnetic fields, as found in high-intensity laser-matter interactions and astrophysical environments such as neutron star magnetospheres. When the energy of the photon becomes comparable to that of the electron, it is necessary to use quantum electrodynamics (QED) to describe the dynamics accurately. However, computing the appropriate scattering matrix element from strong-field QED is not generally possible due to multiparticle effects and the complex structure of the electromagnetic fields. Therefore, these interactions are treated semiclassically, coupling probabilistic emission events to classical electrodynamics using rates calculated in the locally constant field approximation. Here, we provide comprehensive benchmarking of this approach against the exact QED calculation for nonlinear Compton scattering of electrons in an intense laser pulse. We find agreement at the percentage level between the photon spectra, as well as between the models' predictions of absorption from the background field, for normalized amplitudes a0 > 5. We discuss possible routes towards improved numerical methods and the implications of our results for the study of QED cascades.
Highlights
Petawatt and multipetawatt laser facilities that reach focussed intensities in excess of $1022 W cmÀ2 (Refs. 1 and 2) hold great promise for the study of the interaction of charged particles with electromagnetic fields of unprecedented strength.3–6 In these environments, the recoil associated with emission of radiation, known as radiation reaction, can become so large that it dominates the particle dynamics.7,8 when the energy of individual photons of this radiation becomes comparable to that of the emitting particle, it becomes essential to incorporate quantum effects on this radiation reaction9 in our modelling of plasmas as sources of high-energy photons,10 electron-positron pairs,11,12 or as laboratory analogues of high-field astrophysical environments.13,14Strong-field quantum electrodynamics (QED) is not used directly to model these kinds of interactions for a number of reasons
We will consider dimensionless amplitudes in the range of 5 a0 30, which covers the transition between the weakly and highly nonlinear classical regimes, and restrict the laser duration to be s 1⁄4 2 or 3 so that the expected number of photons is of order one. This is because our QED calculations are performed for single scattering only, and so that we can gather sufficient statistics in the semiclassical simulations
The selection and scaling scheme we have presented here could be extended to comparisons with QED calculations of double, triple, etc., nonlinear Compton scattering
Summary
Petawatt and multipetawatt laser facilities that reach focussed intensities in excess of $1022 W cmÀ2 (Refs. 1 and 2) hold great promise for the study of the interaction of charged particles with electromagnetic fields of unprecedented strength. In these environments, the recoil associated with emission of radiation, known as radiation reaction, can become so large that it dominates the particle dynamics. when the energy of individual photons of this radiation becomes comparable to that of the emitting particle, it becomes essential to incorporate quantum effects on this radiation reaction in our modelling of plasmas as sources of high-energy photons, electron-positron pairs, or as laboratory analogues of high-field astrophysical environments.13,14Strong-field QED is not used directly to model these kinds of interactions for a number of reasons. 1 and 2) hold great promise for the study of the interaction of charged particles with electromagnetic fields of unprecedented strength.3–6 In these environments, the recoil associated with emission of radiation, known as radiation reaction, can become so large that it dominates the particle dynamics.. It is generally assumed that back-reaction effects may be neglected This is especially important when considering QED cascades, in which the initial state contains a single electron, positron, or photon and the final state many of these, because we expect significant absorption of energy from the background. (See Ref. 26 for analysis beyond this approximation.) Even in the absence of significant depletion, the multiplicity alone makes the calculation of a cascade within strong-field QED extremely challenging. State-of-the-art results are those in which the final state contains two additional particles, such as double Compton scattering and trident pair creation from single electrons
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