Nonlinear relativistic electron Thomson Scattering for laser radiation with orbital angular momentum

Abstract

The classical nonlinear incoherent Thomson Scattering (TS) power spectrum from free relativistic electrons moving in a laser beam with orbital angular momentum (OAM) is investigated. The main focus in this paper is on the TS process as a diagnostic technique for this type of beams. Linearly polarized incoming radiation and electrons of very low initial kinetic energy are considered. Averaged spectra from electrons randomly covering the transverse laser pattern have different shape in the case of a beam with OAM as compared with the TEM00 case (with vanishing net OAM). Hence, spectrally resolved measurements are needed to discriminate between both cases. If electrons are distributed over the laser spot as thin stripes at a given angle with respect to the polarization direction, computations show non-trivial angular dependencies of integrated power of a laser with OAM as compared with the TEM00 mode. An experimental test of the OAM state of a laser beam is proposed based on these results. The numerical code developed is general enough to deal with more complex polarization states of the laser beam and/or electrons having arbitrary initial kinetic energies.