Ultrafast polarization of an electron beam in an intense bichromatic laser field

Abstract

Here, we demonstrate the radiative polarization of high-energy electron beams in collisions with ultrashort pulsed bi-chromatic laser fields. Employing a Boltzmann kinetic approach for the electron distribution allows us to simulate the beam polarization over a wide range of parameters and determine the optimum conditions for maximum radiative polarization. Those results are contrasted with a Monte-Carlo algorithm where photon emission and associated spin effects are treated fully quantum mechanically using spin-dependent photon emission rates. The latter method includes realistic focusing laser fields, which allows us to simulate a near-term experimentally feasible scenario of a 8 GeV electron beam scattering from a 1 PW laser pulse and provide a measurement that would verify the ultrafast radiative polarization in high-intensity laser pulses that we predict. Aspects of spin dependent radiation reaction are also discussed, with spin polarization leading to a measurable (5%) splitting of the energies of spin-up and spin-down electrons.One of the driving forces in the development of petawatt class laser systems [1-3] is related to novel laserplasma based accelerator concepts. Recent laser wakefield acceleration experiments have demonstrated acceleration of electrons up to 8 GeV energy in a single stage [4] and may enable future novel TeV electron-positron colliders for high-energy physics [5,6]. Spin-polarized beams are crucial for high-energy collider applications, for instance in order to suppress the standard-model background in searches for new physics beyond the standard model [7,8]. Studying the dynamics of spin-polarized electrons in a plasma wakefield is therefore important [9][10][11]. Spin forces have been suggested to be important in both astrophysical systems and high intensity laserplasma interactions [12]. With increasing interest in high intensity laser-plasma interactions, it is essential to understand lepton spin effects on the overall plasma dynamics through radiation reaction-because of the spindependence in the photon emission rates-and electronpositron pair generation [13]. There has been notable recent interest in spin polarization of leptons in highintensity laser interactions [14][15][16].It is known that initially unpolarized lepton beams radiatively polarize in storage rings due to asymmetries in the rates for synchrotron emission; the so-called Sokolov-Ternov effect [17][18][19]. As a result, their projected spins end up being predominantly anti-aligned with the magnetic field direction. For most machines this is a slow process, with a timescale of minutes or hours, scaling as T ∝ γ/χ 3 [18,19], where χ = e 2 p.F 2 .p/m 3 = γ|e|B/m 2 1 is the quantum nonlinearity parameter, with the field strength tensor F and electron mass m, charge e and four-momentum p µ with Lorentz factor γ = p 0 /m [20].We previously demonstrated that a similar spin-up electrons down electrons FIG. 1. Electrons propagating through a bi-chromatic laser pulse perform spin-flips dominantly in certain phases ϕ of the f...

Polarized Ultrashort Brilliant Multi-GeV γ Rays via Single-Shot Laser-Electron Interaction

“…The electron initial kinetic energy is ε 0 = 10 GeV, the angular divergence 0.2 mrad, and the energy spread ∆ε 0 /ε 0 = 0.06. Such electron bunches are achievable via laser wakefield acceleration [61,62] with further radiative polarization [50,63] or alternatively, via directly wakefield acceleration of LSP electrons [64].…”

Generation of polarized particle beams at relativistic laser intensities

“…(3) Radiative polarization of high-energy electron beams in collisions with ultra-short pulsed bichromatic (twocolor) laser fields has been proposed by Seipt et al [40] and Song et al [41] . The scheme is depicted in Figure 3 and is based on the asymmetric distribution of the Figure 1.…”

“…Electrons propagating through a bichromatic laser pulse perform spin-flips dominantly in certain phases of the field: electrons initially polarized along the +y direction (yellow trajectories) flip their spin to down (trajectory colored purple) dominantly when B y > 0, and this is where 1ω and 2ω add constructively (blue contours). The opposite spinflip dominantly happens when B y < 0, where the 1ω and 2ω components of the laser are out of phase (orange contours) [40] .…”

Ultrarelativistic polarized positron jets via collision of electron and ultraintense laser beams

“…This is in contrast to [51], where asymmetric two-color laser field is applied for positron polarization, yielding though considerable less polarization and larger angular spreading. A similar two-color laser model is proposed to polarize electrons as well [52,53]. Our theoretical analysis is based on Monte Carlo simulations of the particles' spin and space-time dynamics taking into account the radiation and pair production processes in spin resolved manner.…”