近日，上海交通大学物理与天文学院的张东方与德国电子同步加速器自由电子激光科学中心的Franz X. Kärtner等人合作并取得一项新进展。经过不懈努力，他们研制出高梯度太赫兹驱动的超快光电子枪。相关研究成果已于2024年5月14日在国际知名学术期刊《自然—光子学》上发表。

该研究团队提出一种新型毫米尺度的多电池波导太赫兹驱动光电子枪，其特点在于通过场增强提升电子能量、可移动阴极实现加速阶段的精准控制，以及多电池结构实现精细光束控制。短波长驱动使得峰值加速度梯度高达约3GVm^-1。利用微焦耳级单周期太赫兹脉冲，研究人员成功演示了能量高达约14keV、能量分散1%、横向发射度约为0.015mmmrad的高质量电子束。

进一步地，研究人员采用高度集成的再聚束电池，将电子束进一步压缩至约167fs，电荷量约10fC。这一技术突破不仅实现了单晶硅的高质量衍射图案和铜网的投影显微镜图像，而且能够以高时空分辨率揭示光激发后铜网上带电粒子形成的瞬态径向电场，为基于等离子体的光束操纵提供了一种潜在的方案。

总的来说，这些成果在太赫兹驱动电子枪的能量、场梯度、光束质量和控制方面均创下了新纪录，使得电子投影显微镜和衍射的实际应用成为可能。这不仅是全光太赫兹驱动电子器件发展的关键里程碑，也充分验证了该技术的成熟度和在精密应用中的巨大潜力。

据悉，基于太赫兹(THz)的电子加速技术有潜力成为下一代经济高效的紧凑型电子源技术。虽然原理验证演示已经证明了许多太赫兹驱动加速器组件的可行性，但在要求苛刻的超快应用中，具有足够亮度、能量和控制的太赫兹驱动光电子枪尚未实现。

附：英文原文

Title: High gradient terahertz-driven ultrafast photogun

Author: Ying, Jianwei, He, Xie, Su, Dace, Zheng, Lingbin, Kroh, Tobias, Rowher, Timm, Fakhari, Moein, Kassier, Gnther H., Ma, Jingui, Yuan, Peng, Matlis, Nicholas H., Kartner, Franz X., Zhang, Dongfang

Issue&Volume: 2024-05-14

Abstract: Terahertz (THz)-based electron acceleration has potential as a technology for next-generation cost-efficient compact electron sources. Although proof-of-principle demonstrations have proved the feasibility of many THz-driven accelerator components, THz-driven photoguns with sufficient brightness, energy and control for use in demanding ultrafast applications have yet to be achieved. Here we present a novel millimetre-scale multicell waveguide-based THz-driven photogun that exploits field enhancement to boost the electron energy, a movable cathode to achieve precise control over the accelerating phase as well as multiple cells for exquisite beam control. The short driving wavelength enables a peak acceleration gradient as high as ~3GVm^-1. Using microjoule-level single-cycle THz pulses, we demonstrate electron beams with up to ~14keV electron energy, 1% energy spread and ~0.015mmmrad transverse emittance. With a highly integrated rebunching cell, the bunch is further compressed by about ten times to 167fs with ~10fC charge. High-quality diffraction patterns of single-crystal silicon and projection microscopy images of the copper mesh are achieved. We are able to reveal the transient radial electric field developed from the charged particles on a copper mesh after photoexcitation with high spatio-temporal resolution, providing a potential scheme for plasma-based beam manipulation. Overall, these results represent a new record in energy, field gradient, beam quality and control for a THz-driven electron gun, enabling real applications in electron projection microscopy and diffraction. This is therefore a critical step and milestone in the development of all-optical THz-driven electron devices, validating the maturity of the technology and its use in precision applications.

DOI: 10.1038/s41566-024-01441-y

Source: https://www.nature.com/articles/s41566-024-01441-y