Numerical investigation of an anti-symmetric nanophotonic structure for accelerating sub-relativistic electron beams

Abstract

This study investigates an anti-symmetrically positioned nanophotonic dual-pillar structure, in which the dielectric and vacuum components are evenly distributed along the direction of electron propagation, with each dielectric pillar facing a vacuum region. Our numerical simulation results show that the previously proposed symmetric dielectric grating structure, where dielectric pillars facing each other are alternated with vacuum gaps, is accompanied by a deceleration region, preventing the achievement of high gradients during the acceleration process. By contrast, the anti-symmetric grating structure eliminates the deceleration field and generates a uniformly distributed acceleration field. This requires that the two oppositely directed laser beams crossing the structure in the transverse region must have a phase shift of π in the anti-symmetric case. This structure has significant potential for accelerating sub-relativistic electron beams. In this numerical simulation, the initial energy of the sub-relativistic electron beams is selected as 79 keV. The acceleration gradient provided by the symmetric design for sub-relativistic electrons is approximately 70 MeV/m; however, the anti-symmetric structure can provide a maximum acceleration gradient of up to ∼430 MeV/m.