Generation of Isolated Collimated Polarized $γ$-ray Beams via Spatiotemporal Optical Vortex Modulation

Abstract

Attosecond, collimated, bright, polarized $γ$-ray sources are in high demand across nuclear physics, astrophysics, and high-energy physics. However, realizing attosecond duration, high collimation, high brilliance, and high polarization simultaneously within a single isolated source remains an outstanding challenge, owing to the inherent trade-offs between beam trapping and radiative dynamics. Here, we propose a novel scheme to generate an isolated, collimated, high-brilliance, polarized attosecond $γ$-ray beam from conventional solid foils irradiated by a linearly polarized spatiotemporal optical vortex (STOV) laser pulse accessible in Lab. Three-dimensional spin-resolved particle-in-cell simulations reveal that this relativistic-intensity STOV pulse can trap and accelerate electrons at its spatiotemporal singularity, producing a compact isolated electron bunch. This electron bunch subsequently undergoes head-on collision with the reflected laser pulse, which generates isolated $γ$-ray beams through nonlinear Compton scattering. With a peak intensity of $7\times10^{21}$ W/cm$^2$, we observe an isolated collimated ($\sim1.5^{\circ}$) $γ$-ray beam with an average linear polarization of $>60\%$ and a duration of $\sim$500 attoseconds. This approach is feasible with current or upcoming laser facilities and robust against variations in laser and target parameters, highlighting the capability of spatiotemporal structured light field modulation to address outstanding problems in plasma physics.