Direct laser acceleration of non-relativistic electrons at a photonic structure

Abstract

Summary form only given. Acceleration of charged particles exploiting the large optical field strength of short laser pulses and the proximity of a dielectric structure has been envisioned to revolutionize particle accelerators [1,2]. Direct acceleration by the optical carrier field of the laser can take place in the vicinity of a grating, also known as the inverse Smith-Purcell effect [3], which has been observed at a metal grating with a terahertz radiation source, however, the acceleration gradient was small (keV/m) [4]. Dielectrics allow much larger acceleration gradients and hence much smaller accelerators due to their orders of magnitude higher damage threshold in the optical regime as compared to metals. Using dielectric gratings as an optical accelerator has been proposed by Plettner et al. [5]. We observe direct laser acceleration of non-relativistic 28 keV electrons close to a single fused-silica transmission grating that is illuminated by Titanium:sapphire laser pulses from below (see Fig. 1a-c). Our findings represent the first demonstration of realistically scalable laser acceleration and of the inverse Smith-Purcell effect in the optical regime. The observed maximum acceleration gradient of 25 MeV/m (see Fig. 1d) is already comparable to state-of-the-art linear accelerators operating with radio-frequency fields. Our work represents the decisive step towards an all-optical linear accelerator that may allow building table-top free electron lasers [6] and other electron optical devices.