Planar wiggler as a tool for generating hard twisted photons

Abstract: Simple formulas for the probability of radiation of twisted photons by scalar and Dirac particles with quantum recoil taken into account are derived. We show that the quantum recoil does not spoil the selection rule for the forward radiation of twisted photons in the planar undulator: $m+n$ is an even number, where $n$ is the harmonic number and $m$ is the projection of the total angular momentum of the radiated twisted photon. The explicit formulas for the radiation probability of twisted photons produced in the planar wiggler are obtained with account for the quantum recoil. The radiation of twisted photons by GeV electrons in the planar wiggler and in the crystalline undulator is investigated.