Coherent nonlinear Thomson scattering of Laguerre-Gauss beams on an electron sheet

TL;DR

This paper investigates the coherent nonlinear scattering of Laguerre-Gauss laser beams on an electron sheet, revealing the generation of structured, helical harmonic radiation carrying orbital angular momentum, with theoretical and numerical analysis aligning with experimental observations.

Contribution

It introduces a theoretical and numerical framework for analyzing helical harmonic generation from Laguerre-Gauss beams scattering on electrons, highlighting the spatial and angular structure of the emitted radiation.

Findings

Radiation is emitted mainly in a narrow forward cone.

Harmonics carry orbital angular momentum with helical structures.

Results agree with experimental observations of OAM photon generation.

Abstract

We present a study of the scattering of a monochromatic helical laser beam, described by a Laguerre-Gauss solution of the Maxwell equations, on an electron sheet, initially at rest in the focal plane of the laser; the interaction is described in the framework of a local plane wave approximation. We calculate the scattered electromagnetic field observed in an arbitrary point at a large distance from the laser focal spot, by adding coherently the contributions of each electron in the electron sheet. Due to the interference effects, the radiation is emitted only into the forward direction, within a narrow cone, and it has a spatial structure that we analyze theoretically and numerically. For circularly polarized incident fields, the structure is also helical, with a helical index which depends on the helical index of the incident radiation and the harmonic order. These structures can be observed experimentally, as each harmonic order is emitted with a different frequency, and within cones of different opening angles. Our findings are in agreement with experimental results in the literature which demonstrate the generation of OAM carrying photons by radiation scattering on electrons.