Multi-cycle THz driven electron acceleration and THz-energy recycling

Electron accelerators powered by terahertz (THz) radiation have recently emerged as promising candidates for next-generation compact electron sources. Although initial work has demonstrated impressive capabilities for acceleration and beam manipulation, the THz drivers used have been single-cycle pulses which are easier to generate at high field strengths, but are less favorable for scaling to long interaction lengths. Here we report, for the first time, use of narrow-band multi-cycle THz drivers for electron manipulation (acceleration, compression, and focusing). Moreover, we propose and demonstrate a novel scheme of cascaded acceleration, uniquely suited to multicycle drivers, for increasing the interaction length by re-cycling and- phasing the interaction. This work opens new possibilities for the design of THz based accelerators.