Generation of twisted γ-ray radiation by nonlinear Thomson scattering of twisted light

Interaction of twisted strong laser radiation with electrons in the classical regime is considered.We investigate transfer of the angularmomentumof absorbed laser photons to the emitted radiation.An interaction regime is considered where radiation reaction is negligible and the formation length of radiation is comparable to or larger than the laser wavelength.The latter condition ensures that the structure of the laser field plays a role in the electron dynamics during the formation of radiation.Wedistinguish the case of a single electron from that of an electron beam.For a single electron,the spin angular momentum of the driving laser photons is transferred to the radiation field,while the orbital angular momentum of the laser field is not.We conclude that in the classical regime,to imprint the angular momentum of twisted light on radiation,an electron beam is a prerequisite.In the latter case,nonlinear Thomson scattering of twisted light off an ultrarelativistic electron beam produces high-frequency radiation that is twisted,with a topological charge proportional to the harmonic order.

Photon polarization effects in polarized electron–positron pair production in a strong laser field

Deep understanding of the impact of photon polarization on pair production is essential for the efficient generation of laser-driven polarized positron beams and demands a complete description of polarization effects in strong-field QED processes.Employing fully polarization-resolved Monte Carlo simulations,we investigate correlated photon and electron(positron)polarization effects in the multiphoton Breit–Wheeler pair production process during the interaction of an ultrarelativistic electron beam with a counterpropagating elliptically polarized laser pulse.We show that the polarization of e−e+pairs is degraded by 35%when the polarization of the intermediate photon is resolved,accompanied by an∼13%decrease in the pair yield.Moreover,in this case,the polarization direction of energetic positrons at small deflection angles can even be reversed when high-energy photons with polarization parallel to the laser electric field are involved.

Energy enhancement of laser-driven ions by radiation reaction and Breit-Wheeler pair production in the ultra-relativistic transparency regime

The impact of radiation reaction and Breit±Wheeler pair production on the acceleration of fully ionized carbon ions driven by an intense linearly polarized laser pulse has been investigated in the ultra-relativistic transparency regime.Against initial expectations, the radiation reaction and pair production at ultra-high laser intensities are found to enhance the energy gained by the ions. The electrons lose most of their transverse momentum, and the additionally produced pair plasma of Breit±Wheeler electrons and positrons co-streams in the forward direction as opposed to the existing electrons streaming at an angle above zero degree. We discuss how these observations could be explained by the changes in the phase velocity of the Buneman instability, which is known to aid ion acceleration in the breakout afterburner regime, by tapping the free energy in the relative electron and ion streams. We present evidence that these non-classical effects can further improve the highest carbon ion energies in this transparency regime.

Generation of arbitrarily polarized GeV lepton beams via nonlinear Breit-Wheeler process

Generation of arbitrarily spin-polarized electron and positron beams has been investigated in the single-shot interaction of high-energy polarized r-photons with an ultraintense asymmetric laser pulse via nonlinear Breit-Wheeler pair production.We develop a fully spin-resolved semi-classical Monte Carlo method to describe the pair creation and polarization.In the considered general setup,there are two sources of the polarization of created pairs:the spin angular momentum transfer from the polarized parent-photons,as well as the asymmetry and polarization of the driving laser field.This allows to develop a highly sensitive tool to control the polarization of created electrons and positrons.Thus,dense GeV lepton beams with average polarization degree up to about 80%,adjustable continuously between the transverse and longitudinal components,can be obtained by our all-optical method with currently achievable laser facilities,which could find an application as injectors of the polarized e^(+)e^(-)collider to search for new physics beyond the Standard Model.