• High Power Laser Science and Engineering
  • Vol. 8, Issue 4, 04000e36 (2020)
Markus Büscher1、2、*, Anna Hützen1、2, Liangliang Ji3、4、*, and Andreas Lehrach5、6
Author Affiliations
  • 1Peter Grünberg Institut (PGI-6), Forschungszentrum Jülich, Jülich, Germany
  • 2Institut für Laser- und Plasmaphysik, Heinrich-Heine-Universität Düsseldorf, Düsseldorf, Germany
  • 3State Key Laboratory of High Field Laser Physics, Shanghai Institute of Optics and Fine Mechanics, Chinese Academy of Sciences, Shanghai201800, China
  • 4CAS Center for Excellence in Ultra-intense Laser Science, Shanghai201800, China
  • 5JARA-FAME (Forces and Matter Experiments), Forschungszentrum Jülich and RWTH Aachen University, Aachen, Germany
  • 6Institut für Kernphysik (IKP-4), Forschungszentrum Jülich, Jülich, Germany
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    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[34]. OAP, optical parametric amplification.
    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[34]. OAP, optical parametric amplification.
    Schematic representation of electron spin polarization employing the standing wave of two colliding, circularly polarized laser pulses[39].
    Fig. 2. Schematic representation of electron spin polarization employing the standing wave of two colliding, circularly polarized laser pulses[39].
    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 ω and 2ω components of the laser are out of phase (orange contours)[40].
    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)[40].
    Scheme for laser-based polarized positron beam production[42].
    Fig. 4. Scheme for laser-based polarized positron beam production[42].
    Sketch of the all-optical laser-driven polarized electron acceleration scheme using a pre-polarized target[46]. LG, Laguerre–Gaussian; OAP, optical parametric amplification.
    Fig. 5. Sketch of the all-optical laser-driven polarized electron acceleration scheme using a pre-polarized target[46]. LG, Laguerre–Gaussian; OAP, optical parametric amplification.
    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[54].
    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[54].
    Measured 3,4He2+ energy spectra accelerated from unpolarized helium gas jets[56]. IP, image plate.
    Fig. 7. Measured 3,4He2+ energy spectra accelerated from unpolarized helium gas jets[56]. IP, image plate.
    Sketch of the interplay between single particle trajectories (blue), spin (red) and radiation (yellow)[48].
    Fig. 8. Sketch of the interplay between single particle trajectories (blue), spin (red) and radiation (yellow)[48].
    (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[34].
    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[34].
    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(χ0 = 1) = 16.5[40].
    Fig. 10. 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., a00 = 1) = 16.5[40].
    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[41].
    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[41].
    Prediction from Wu et al.[46] 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. 12. Prediction from Wu et al.[46] 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.
    Electron polarization distributions in the transverse phase space during laser-wakefield acceleration[49].
    Fig. 13. Electron polarization distributions in the transverse phase space during laser-wakefield acceleration[49].
    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[53].
    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[53].
    (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[54].
    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[54].
    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[56].
    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[56].
    Perspective view of the 3D model of the fully mounted magnetic system inside the PHELIX chamber[57,67].
    Fig. 17. Perspective view of the 3D model of the fully mounted magnetic system inside the PHELIX chamber[57,67].
    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[46].
    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[46].
    Technical drawing of the optical setup including the JuSPARC_MIRA laser system and the target chamber for the polarized proton target[64].
    Fig. 19. Technical drawing of the optical setup including the JuSPARC_MIRA laser system and the target chamber for the polarized proton target[64].
    Schematic view of the interaction chamber for production and storage of polarized H2, D2, HD and foils[71].
    Fig. 20. Schematic view of the interaction chamber for production and storage of polarized H2, D2, HD and foils[71].
    Schematic view of the setup for proton polarization measurements by Raab et al.[72] 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.
    Fig. 21. Schematic view of the setup for proton polarization measurements by Raab et al.[72] 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.