Numerical investigation of asymmetric nanophotonic structure for accelerating sub-relativistic electron beams

We proposed an asymmetrically placed nanophotonic dual-pillar structure, the dielectric part and the vacuum part of the structure are evenly distributed in the direction of electron propagation. This structure is optimized for sub-relativistic electron acceleration. We discuss numerical simulation results, which show that the previously proposed dielectric grating structure is accompanied by a deceleration region that is not conducive to achieving high gradients during the entire acceleration process. By our scheme, the deceleration field is completely eliminated, and a uniform distribution of acceleration field is produced in the acceleration channel of the asymmetric grating structure. Our structure requires two laser pulses with a specific phase difference injected from both sides of the structure to achieve the optimization of the acceleration field. The structure has great potential in the acceleration of sub-relativistic electron beams. To show the comparative advantages of this asymmetric design, we also numerically investigated the symmetric structure. The acceleration gradient provided by the symmetric structure for sub-relativistic electrons is about 70 MeV/m, however, the maximum acceleration gradient provided by asymmetric structure for sub-relativistic electrons is up to ∼430 MeV/m.