Violation of the transit-time limit toward generation of ultrashort electron bunches with controlled velocity chirp

Abstract

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.

Proton acceleration from overdense plasma target interacting with shaped laser pulses in the presence of preplasmas

“…The fields on particles are area (volume)-weighted in the rectangular meshes. This PIC code was successfully used in various underdense plasma simulations [43,44,[48][49][50] as well as in proton acceleration simulations [51].…”

Simulation of laser-induced rectification in a nano-scale diode

“…Such semiconductorbased devices have been the backdrop of the advancing field of electronics for many years; however, as the push for ultrafast operating speeds approaches the petahertz range, 1 the limited electron transport velocity of semiconductor transistors presents a formidable obstacle. Recent interest in electron photo-emission from metal nanotips, [2][3][4][5] motivated by improved ultrafast laser-guidance of electrons, [6][7][8][9][10][11][12][13] has inspired research pointing back in the direction of vacuum transport as a path towards achieving such higher speeds, with some prototype transistor devices being fabricated in the last few years. [14][15][16][17] In this study, we focus on the template of Higuchi et al 17 who take advantage of asymmetric near-field enhancement of two facing tungsten tips in order to achieve laser-driven rectification.…”