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Abstract

Gamma-ray beams with large angular momentum are a very valuable tool to study
astrophysical phenomena in a laboratory. We investigate generation of
well-collimated $\gamma$-ray beams with a very large orbital angular momentum
using nonlinear Compton scattering of a strong laser pulse of twisted photons
at ultra-relativistic electrons. Angular momentum conservation among absorbed
laser photons, quantum radiation and electrons are numerically demonstrated in
the quantum radiation dominated regime. We point out that the angular momentum
of the absorbed laser photons is not solely transferred to the emitted
$\gamma$-photons, but due to radiation reaction shared between the
$\gamma$-photons and interacting electrons. The efficiency of the angular
momentum transfer is optimized with respect to the laser and electron beam
parameters. The accompanying process of electron-positron pair production is
furthermore shown to enhance the orbital angular momentum gained by the
$\gamma$-ray beam.