Laser-driven positron sources, characterized by short pulse width, small focal spot and high energy, are promising for potential applications, e.g. electron–positron collider and positron annihilation spectroscopy. Currently, the generation of such positron beams has achieved significant progress via direct or indirect manners. However, positron beams from direct method usually have large divergence angles (typically>20°), which results in broadening pulse width and deteriorating divergence angle during energetic positron transport. In order to improve the quality of positron beams, external magnetic fields or self-generated target sheath fields are utilized. However, due to broad energy spectrum of positron beams, temporal lengthening and density decreasing occur. Here, we propose a novel method to manipulate the positrons by using a left-hand circularly-polarized Laguerre–Gaussian (LG) laser pulse. Using the LG laser with an intensity of 1.2×10²¹ W∙cm⁻² and a duration of a few cycles, three-dimensional particle-in-cell simulations reveal that isotropic hot positrons can be effectively captured, collimated, compressed, and accelerated due to the unique field structure of the LG laser. A high-quality positron bunch is obtained with a peak divergence angle of 1°, an average pulse duration of 0.5 fs, a maximum energy of 450 MeV, and a density of 70 times that of the initial electron source. A damping vibration model is also formulated to explain qualitatively the quality improvement of the positrons.
 

Capture; Hot positron; Laguerre-Gaussian laser pulse