Surface Plasmons in Strong Fields and Their Applications to Beam Acceleration

Surface plasmons (SPs) are collective oscillations of free electrons that are confined to the interface between conducting (e.g., plasma) and dielectric (e.g., vacuum) materials. When SPs couple strongly with electromagnetic waves (photons), they form hybrid quasiparticles called surface plasmon polaritons (SPPs). This coherent behaviour can be driven by external beams such as photons or charged particle beams, through the long-range Coulomb interactions between conduction electrons. When external sources are highly intense, with strong fields that can quickly accelerate free electrons to relativistic speeds, the dynamics of SPs differ from those in the low-energy case. In this chapter, we demonstrate that the SPs driven by high-intensity laser or particle beams can provide TV/m-level electromagnetic fields. Charged particles can be efficiently accelerated if they are properly placed and maintained in these fields. Three different mechanisms of SP-based particle acceleration are then proposed by using particle-in-cell simulations, including leaky and bubble wakefield acceleration and direct electron acceleration due to the resonant coupling of SPs. These results demonstrate that the efficient excitation of SPs in strong fields could provide a promising solution for the next generation of ultra-compact particle accelerators. It can offer unprecedented benefits in various advanced applications due to its ultra-high acceleration gradient and flexibility.