Terahertz-driven nanotip field-emission electron gun and cascaded acceleration

This paper reports two versions of terahertz (THz)-driven nanotip field-emission electron guns: single-layer reflective guns (SLRGs) and double-layer reflective guns (DLRGs). SLRGs employ a reflective structure to superimpose the initial and subsequent half-cycles of the THz electric field, enhancing the field amplitude and acceleration efficiency. Experimental results demonstrate its superior acceleration efficiency over a single-layer non-reflective gun (SLNRG) with identical input, providing direct validation of the concept. Theoretically, the single-feed SLRG can match the dual-feed SLNRG's acceleration efficiency while offering significantly simpler synchronization. DLRGs comprise two independent reflective structures, each with individual THz injection. By precisely scanning the delay between the two incident THz beams, we demonstrate THz-driven cascaded electron acceleration, which represents a direct experimental demonstration and a pioneering step of cascaded acceleration in THz-driven electron sources. The experimental results of DLRGs align closely with the results of electron dynamics predicted by simulations, establishing the foundation for developing multi-layer high-acceleration-efficiency THz-driven high-energy electron guns. The ability to manipulate the THz for each layer individually holds promising potential for improving the performance of THz electron guns.