Instruct: Identify the main and secondary category of Arxiv papers based on the titles and abstracts
Query: Generation of GeV positron and {\gamma}-photon beams with controllable
  angular momentum by intense lasers   Although several laser-plasma-based methods have been proposed for generating
energetic electrons, positrons and {\gamma}-photons, manipulation of their
microstructures is still challenging, and their angular momentum control has
not yet been achieved. Here, we present and numerically demonstrate an
all-optical scheme to generate bright GeV {\gamma}-photon and positron beams
with controllable angular momentum by use of two counter-propagating
circularly-polarized lasers in a near-critical-density plasma. The plasma acts
as a "switching medium", where the trapped electrons first obtain angular
momentum from the drive laser pulse and then transfer it to the
{\gamma}-photons via nonlinear Compton scattering. Further through the
multiphoton Breit-Wheeler process, dense energetic positron beams are
efficiently generated, whose angular momentum can be well controlled by
laser-plasma interactions. This opens up a promising and feasible way to
produce ultra-bright GeV {\gamma}-photons and positron beams with desirable
angular momentum for a wide range of scientific research and applications.

28
The categories of this paper are: alg-geom
10
The categories of this paper are: q-bio
33
The categories of this paper are: plasm-ph
18
The categories of this paper are: econ
19
The categories of this paper are: eess
7
The categories of this paper are: hep-th
23
The categories of this paper are: solv-int
0
The categories of this paper are: hep-ph
8
The categories of this paper are: hep-ex
31
The categories of this paper are: ao-sci
32
The categories of this paper are: atom-ph
1
The categories of this paper are: cs
27
The categories of this paper are: comp-gas
9
The categories of this paper are: nlin
29
The categories of this paper are: funct-an
26
The categories of this paper are: bayes-an