Vacuum Laser Acceleration of electrons by a nano-needle in tightly focused short-pulse laser

High-energy electron beams have a plethora of applications from industrial to medical and academic research. With the state-of the-art PW laser facilities, such electron beams can be generated by intense laser pulses interacting with matter, either by the field of the laser or by the field in plasma (such as wakefields). In Vacuum Laser Acceleration (VLA), electrons loaded in the fast-varying high laser field gain energy directly from the laser. By using nano-structured target, such as a needle, one can facilitate VLA [1, 2]. We investigated electron spectra from a sub-two-cycle laser pulse incident on 100nm tungsten tip using 3D PIC simulations at different laser focussing configurations. Behind the acceleration mechanism lies a two-step process: in the first step, there is a nano-photonic emission of relativistic electrons from the target within half an optical cycle. In a second step, these electrons experience vacuum laser acceleration. Our findings are in good agreement with the experiments performed [3].