Synchronous Acceleration of Subrelativistic Particles in an Inverse-Cherenkov Dielectric Laser Accelerator With Tapered Phase Velocity

We propose a dielectric laser acceleration scheme based on the inverse Cherenkov effect, which utilizes a pair of dielectric prisms with customized surfaces for accelerating subrelativistic electrons. This scheme enables the continuous acceleration of subrelativistic electrons by adaptively adjusting the phase velocity of the acceleration wave along its propagation direction in response to the increasing velocity of electrons. The resulting synchronization between the electrons and the acceleration wave ensures that the electrons are continuously accelerated to higher energies without significant phase slippage. We introduce a design method for this acceleration structure based on the adiabatic approximation and provide an example to verify this method through simulations. Simulation results show that a 100-
$\mu \text{m}$
-long structure can continuously accelerate electrons from an initial energy of 100–143.2 keV, and the energy gain far exceeds the maximum energy gain of 9 keV of the nontapered scheme under the same condition. It is worth mentioning that the scheme has the potential to continuously accelerate electrons from an initial energy of 100 keV to near-relativistic energies (>1 MeV). By using mature electron beam lithography, the tapered structure can be integrated into a chip for megaelectronvolt-level tabletop ultrafast electron diffraction.