Fig. 1. (a) Photon emission probability log₁₀ W_i (arbitrary units) and (b) Stokes parameter ξ_3i (i ∈ ↑, ↓) vs emitted photon energy δ_e = ω_γ/ε_i for χ_e = 10. i denotes the electron spin before the emission with respect to the magnetic field direction.

Fig. 2. (a) and (b) Pair production probability dWζ−ζ+ for a polarized photon with (a) ξ₁ = ξ₂ = 0, ξ₃ = 1 and (b) ξ₃ = −1. (c) Positron polarization ζ+=∑ζ−dWζ−↑−dWζ−↓dWζ−↑+dWζ−↓ vs ξ₃ and δ₊. In (a)–(c), χ_γ = 3. (d) Ratio of the photon-polarization-resolved and averaged pair production probabilities dWp(ξ)−dWp(0)dWp(ξ)+dWp(0) vs ξ₃ and δ₊. (e) ζ¯+=∑iζ+(δi)dWp(δi)∑idWp(δi) vs ξ₃ for χ_γ = 0.1 (blue solid curve), 1 (red dashed curve), and 10 (magenta dotted curve). (f) Relative differences ΔN = [N(0) − N(ξ)]/N(ξ) (solid curve) and Δζy=[ζy+(0)−ζy+(ξ)]/ζy+(ξ) (dashed curve) vs χ_γ for ξ₃ = 0.5.

Fig. 3. Scheme for producing polarized positrons via nonlinear Compton scattering of an initially transversely polarized electron off a strong elliptically polarized laser pulse. The energetic gamma photons in the region θyγ<0 have high polarizations up to ξ₃ = 1, resulting in a reduction in or even reversal of polarization of positrons as θy+ decreases.

Fig. 4. (a) Polarized positron density distribution d2N+/dθx+dθy+ (rad⁻²) and (b) averaged polarization degree of y component ζ̄y vs θx+=px/pz (rad) and θy+=py/pz (rad) for photon-polarization-unresolved pair production. (c) and (d) Corresponding plots for photon-polarization-resolved pair production. (e) Polarized positron density distribution dN/dθ_y (rad⁻¹) vs θy+ (rad) for unresolved (solid curve) and resolved (dashed curve) photon polarization. (f) Averaged polarization degree ζ̄y vs θy+ (rad) for unresolved (solid curve) and resolved (dashed curve) photon polarization.

Fig. 5. (a) and (b) log₁₀ dN^γ/dω_γ and averaged Stokes parameter ξ̄3, respectively, of gamma photons emitted in θyγ>0 (solid line) and θyγ<0 (dashed line) vs photon energy ω_γ in |θ_x|, |θ_y| < 10 mrad. (c) and (d) Angular distributions of d2Nγ/dθxγdθyγ (rad⁻²) and ξ̄3, respectively, vs θxγ=kx/kz and θyγ=ky/kz. (e) and (f) Angular distributions of d2Nγ/dθxγdθyγ (rad⁻²) and ξ̄3, respectively, for photons with energy ε > 7.5 GeV [shaded red in (b)].

Fig. 6. (a) Polarized positron density distribution dN/dθy+ (rad⁻¹) and (b) averaged polarization degree ζ̄y vs positron polar angle θy+ (rad) for positrons produced by photons with θyγ>0 (solid curves) and θyγ<0 (dashed curves).

Fig. 7. (a) and (b) log₁₀ dN^γ/dω_γ and averaged Stokes parameter ξ̄3, respectively, of gamma photons emitted in θyγ>0 (solid curves) and θyγ<0 (dashed curves) vs photon energy ω_γ in |θ_x|, |θ_y| < 10 mrad. (c) and (d) Polarized positron density distribution dN/dθ_y (mrad⁻¹) and averaged polarization degree ζ̄y, respectively, vs θ_y (mrad) for unresolved (dashed curves) and resolved (solid curves) photon polarization.

Fig. 8. (a) and (c) Positron number N⁺ in the case of unresolved photon polarization (dashed lines) and in the resolved case (solid lines) and their relative difference ΔN (dotted lines) vs laser intensity a₀ (at a₀ = 50, 100, and 150) and laser pulse duration t_p (at t_p = 3, 5, and 8 T), respectively. (b) and (d) Positron polarization ζ¯y in the case of unresolved photon polarization (dashed lines) and in the resolved case (solid lines) and their relative difference Δζ¯y (dotted lines) vs laser intensity a₀ (at a₀ = 50, 100, and 150) and laser pulse duration t_p (at t_p = 3, 5, and 8 T), respectively. Other parameters are the same as in Fig. 4.