Emittance Reduction of Relativistic Electron Beam Using Optical Bessel Beam

Numerical simulation results are presented that help validate prior published analysis, which showed that the emittance of a relativistic electron beam ($e$-beam) can be reduced by having the electrons counter-propagate through an optical Bessel beam (OBB) created using a radially polarized laser beam. Unlike laser-based schemes for cooling electrons that rely on Compton scattering, the electrons oscillate within the potential well created by the OBB, thereby experiencing a radiation reaction force (RRF) that reduces the transverse momentum of the electrons. The diffraction-free nature of the OBB allows these oscillations to occur over long distances, which helps reduce the required laser peak power. Our simulation demonstrated the contribution of RRF to an emittance reduction of 15% over a 1-m interaction length using a normalized laser amplitude of$a_{0} = 0.22$, and no emittance reduction with the RRF factor excluded. This low value of$a_{0}$permits applying our technique using more readily available lasers than the TW-class lasers that have been proposed for cooling electrons.