Fig. 1. Scenario of the generation of spin-polarized electron beams via nonlinear Compton scattering: a relativistic electron bunch generated by laser-wakefield acceleration collides head-on with an elliptically polarized laser pulse and splits along the propagation direction into two parts with opposite transverse polarization. OAP, optical parametric amplification.
Fig. 2. Schematic representation of electron spin polarization employing the standing wave of two colliding, circularly polarized laser pulses.
Fig. 3. 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 By > 0, and this is where 1ω and 2ω add constructively (blue contours). The opposite spin-flip dominantly happens when By < 0, where the 1ω and 2ω components of the laser are out of phase (orange contours).
Fig. 4. Scheme for laser-based polarized positron beam production.
Fig. 5. Sketch of the all-optical laser-driven polarized electron acceleration scheme using a pre-polarized target. LG, Laguerre–Gaussian; OAP, optical parametric amplification.
Fig. 6. Schematic diagram showing laser acceleration of polarized protons from a dense hydrogen chloride gas target (brown). HCl molecules are initially aligned along the accelerating laser (indicated by the green area) propagation direction via a weak infrared (IR) laser. Blue and white balls represent the nuclei of hydrogen and chlorine atoms, respectively. Before the acceleration, a weak circularly polarized UV laser (purple area) is used to generate the polarized atoms along the longitudinal direction via molecular photo-dissociation. The brown curve indicates the initial density distribution of the gas-jet target. The polarized proton beam is shown on the right (blue) with arrows (red) presenting the polarization direction.
Fig. 7. Measured 3,4He2+ energy spectra accelerated from unpolarized helium gas jets. IP, image plate.
Fig. 8. Sketch of the interplay between single particle trajectories (blue), spin (red) and radiation (yellow).
Fig. 9. (a) Transverse distribution of the electron spin component Sy as a function of the deflection angles θx,y; (b) corresponding logarithmic electron-density distribution. The assumed laser peak intensity is I ≈ 1.38 × 1022 W/cm2 (a0 = 100), wavelength λ = 1 μm, the pulse duration amounts to five laser periods, focal radius 5 μm and ellipticity 0.05. The electron bunch with kinetic energy of 4 GeV and energy spread 6% has an initial angular divergence of 0.3 mrad.
Achievable degree of electron polarization as a function of a quantum nonlinearity parameter χ0
and the bichromaticity parameter c2
(defining the fraction of the total pulse energy in the second harmonic,
). The calculations have been performed for 5 GeV electrons colliding with a 161 fs laser pulse, i.e., a0
= 1) = 16.5
Fig. 11. Average polarization Sy as a function of the relative phase ϕ of the two-color laser pulse for different laser waist radii σ0. The assumed laser intensities are a0,1 = 2a0,2 = 100, I1 = 4I2 = 1.37 × 1022 W/cm2.
Fig. 12. Prediction from Wu et al. for the achievable electron polarization dependent upon the electron current. More than 80% polarization can be achieved when a vortex LG laser pulse is used for the acceleration.
Fig. 13. Electron polarization distributions in the transverse phase space during laser-wakefield acceleration.
Fig. 14. Three-dimensional PIC simulation of proton acceleration assuming a gaseous HCl target with a hydrogen density of 8.5 × 1019 cm−3 and a circularly polarized laser pulse with 800 nm wavelength and a normalized amplitude of a0 = 200. (a) Simulated proton density; (b) polarization as a function of the proton energy.
Fig. 15. (a) Three-dimensional PIC simulation for a gaseous HCl target with molecular density of 1019 cm−3 and 1.3 PW laser with phase-space distribution; (b) spin spread of protons with energy E > 20 MeV on the Bloch sphere.
Fig. 16. Simulated normalized He2+ ion-number density during the passage of a peta-watt laser pulse (6.5 ps after it entered the simulation box at the left boundary) through an unpolarized helium gas jet target. (a) 2%; (b) 3%; (c) 4%; (d) 12% critical density.
Fig. 17. Perspective view of the 3D model of the fully mounted magnetic system inside the PHELIX chamber[57,67].
Fig. 18. The 1064 nm IR laser propagates along the x-axis to align the bonds of the HCl molecules, and then UV light with a wavelength of 213 nm, propagating along the z-axis, is used to photo-dissociate the HCl molecules. A 234.62 nm UV light is used to ionize the Cl atoms. Thermal expansion of the electrons creates a large Coulomb field that expels the Cl ions. A fully polarized electron target is therefore produced for sequential acceleration.
Fig. 19. Technical drawing of the optical setup including the JuSPARC_MIRA laser system and the target chamber for the polarized proton target.
Schematic view of the interaction chamber for production and storage of polarized H2
, HD and
Fig. 21. Schematic view of the setup for proton polarization measurements by Raab et al. Protons are accelerated from an unpolarized gold foil to energies of about 3 MeV, scattered in a silicon foil (scattering target) and finally detected with CR-39 detectors.