Copropagating schemes for dielectric laser accelerators (DLAs).

Laser acceleration of electrons with silicon dielectric structures was demonstrated with accelerating gradients of more than $200 {MeV/m}$. However, many of the proposed configurations (free space coupled gratings, dual pillar, phase reset devices) have an intrinsically limited interaction length, because a transversely incident laser light, impinging laterally along the whole structure's length, is required. In order to obtain both high laser-induced accelerating gradients and adequate interaction length, in this paper we describe extended accelerating structures with collinear propagation of the accelerating electromagnetic field and the particles to be accelerated: both 2D and 3D photonic crystals-based structures, and slot hollow-core waveguides are analyzed and compared in terms of accelerating gradient, damage factor, efficiency, fabrication tolerances and complexity of the laser delivery system.