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Although several laser-plasma-based methods have been proposed for generatingenergetic electrons, positrons and {\gamma}-photons, manipulation of theirmicrostructures is still challenging, and their angular momentum control hasnot yet been achieved. Here, we present and numerically demonstrate anall-optical scheme to generate bright GeV {\gamma}-photon and positron beamswith controllable angular momentum by use of two counter-propagatingcircularly-polarized lasers in a near-critical-density plasma. The plasma actsas a "switching medium", where the trapped electrons first obtain angularmomentum from the drive laser pulse and then transfer it to the{\gamma}-photons via nonlinear Compton scattering. Further through themultiphoton Breit-Wheeler process, dense energetic positron beams areefficiently generated, whose angular momentum can be well controlled bylaser-plasma interactions. This opens up a promising and feasible way toproduce ultra-bright GeV {\gamma}-photons and positron beams with desirableangular momentum for a wide range of scientific research and applications.

Generation of GeV positron and {\gamma}-photon beams with controllable angular momentum by intense lasers