Jeon Seok-Gy, Shin Dongwon, Hur Min Sup
Applied Electromagnetic Wave Research Center, Korea Electrotechnology Research Institute (KERI), Ansan 426-170, Republic of Korea.
Department of Physics, UNIST, Ulsan, 44919, Republic of Korea.
Sci Rep. 2016 Sep 22;6:32567. doi: 10.1038/srep32567.
Various methods to generate ultrashort electron bunches for the ultrafast science evolved from the simple configuration of two-plate vacuum diodes to advanced technologies such as nanotips or photocathodes excited by femtosecond lasers. In a diode either in vacuum or of solid-state, the transit-time limit originating from finite electron mobility has caused spatiotemporal bunch-collapse in ultrafast regime. Here, we show for the first time that abrupt exclusion of transit-phase is a more fundamental origin of the bunch-collapse than the transit-time limit. We found that by significantly extending the cathode-anode gap distance, thereby violating the transit-time limit, the conventional transit-time-related upper frequency barrier in diodes can be removed. Furthermore, we reveal how to control the velocity chirp of bunches leading to ballistic bunch-compression. Demonstration of 0.707 THz-, 46.4 femtosecond-bunches from a 50 μm-wide diode in three-dimensional particle-in-cell simulations shows a way toward simple and compact sources of ultrafast electron bunches for diverse ultrafast sciences.
用于超快科学的各种产生超短电子束团的方法，已从两板真空二极管的简单配置发展到诸如纳米尖端或由飞秒激光激发的光阴极等先进技术。在真空或固态二极管中，由有限电子迁移率引起的渡越时间限制在超快 regime 中导致了时空束团坍缩。在此，我们首次表明，渡越相位的突然排除是束团坍缩比渡越时间限制更根本的起源。我们发现，通过显著延长阴极 - 阳极间隙距离，从而违反渡越时间限制，可以消除二极管中传统的与渡越时间相关的高频障碍。此外，我们揭示了如何控制束团的速度啁啾以实现弹道束团压缩。在三维粒子模拟中从一个 50μm 宽的二极管产生 0.707THz、46.4 飞秒束团的演示，为各种超快科学提供了一种通向简单且紧凑的超快电子束团源的方法。
