Enhancing QED effects by temporal pulse shaping in laser - electron-beam collisions

Quantum stochastic radiation reaction and electron-positron pair production influence the dynamics of plasmas created by laser pulses with high-intensity ≥ 10^23 W/cm^2. Experimental evidence of quantum effects has proven challenging to obtain so far and crucially depend on maximising the electron’s Lorentz invariant non-linearity parameter, χ = ERF/Es, the ratio of the laser electric field observed by the electron in its rest frame ERF to the critical field Es of quantum electrodynamics (QED).
By deriving the average χ ab initio, we find the initial electron energy is crucial as radiation reaction discourages maximum χ before the electrons reach the peak intensity. In the following, we use a QED-PIC code to simulate the collision of a counter-propagating 5 × 10^21 W/cm^2 laser pulse with a 1.5GeV electron-beam. Simulating both symmetric and skewed Gaussian pulses, where the leading edge of the temporal intensity envelope has a fast rise time, leads to an undesirable reduction to the peak intensity I0.
Contrary to the widely accepted result, we show that the optimum temporal envelope to enhance pair production is a short and compressed Gaussian pulse. A skewed Gaussian results in approximately 1.5 × 10^−6 pairs produced per electron and is enhanced by a factor of ~10 to an improvement of 2.0 × 10^-5. To this end, we consider an alternative approach using plasma optics to reach maximum χ to enhance electron-positron pair production.