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Abstract
Radiative polarization of electrons and positrons through the SokolovTernov effect is important for applications in highenergy physics. Radiative spin polarization is a manifestation of quantum radiation reaction affecting the spin dynamics of electrons. We recently proposed that an analog of the SokolovTernov effect could occur in the strong electromagnetic fields of ultrahighintensity lasers, which would result in a buildup of spin polarization in femtoseconds. In this paper, we develop a density matrix formalism for describing beam polarization in strong electromagnetic fields. We start by using the density matrix formalism to study spin flips in nonlinear Compton scattering and its dependence on the initial polarization state of the electrons. Numerical calculations show a radial polarization of the scattered electron beam in a circularly polarized laser, and we find azimuthal asymmetries in the polarization patterns for ultrashort laser pulses. A degree of polarization approaching 9% is achieved after emitting just a single photon. We develop the theory by deriving a local constant crossedfield approximation (LCFA) for the polarization density matrix, which is a generalization of the wellknown LCFA scattering rates. We find spindependent expressions that may be included in electromagnetic chargedparticle simulation codes, such as particleincell plasma simulation codes, using Monte Carlo modules. In particular, these expressions include the spinflip rates for arbitrary initial polarization of the electrons. The validity of the LCFA is confirmed by explicit comparison with an exact QED calculation of electron polarization in an ultrashort laser pulse.
Original language  English 

Article number  023417 
Number of pages  19 
Journal  Physical Review A 
Volume  98 
Issue number  2 
DOIs  
Publication status  Published  20 Aug 2018 
Bibliographical note
©2019. The Author(s)Profiles
Projects
 1 Finished

LaserPlasma Interactions at the Intensity Frontier: the Transition to the QEDPlasma Regime
1/07/15 → 31/08/20
Project: Research project (funded) › Research