Journal Article

High gradient terahertz-driven ultrafast photogun

Matlis, Nicholas H., Zheng, Lingbin, Zhang, Dongfang, Su, Dace, Kärtner, Franz X., Yuan, Peng, Kassier, Günther H., Kroh, Tobias, Fakhari, Moein, Rohwer, Timm, He, Xie, Ma, Jingui, Ying, Jianwei

2024

Overview

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 ~3 GV m −1 . Using microjoule-level single-cycle THz pulses, we demonstrate electron beams with up to ~14 keV electron energy, 1% energy spread and ~0.015 mm mrad transverse emittance. With a highly integrated rebunching cell, the bunch is further compressed by about ten times to 167 fs with ~10 fC 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. A terahertz-driven photogun with field gradients of 3 GV m −1 is demonstrated by using a few microjoules of single-cycle terahertz radiation. The emitted electrons are accelerated up to 14 keV and can be focused down to 90 μm. The electron bunch is further compressed to 167 fs.

• Publisher: Nature Publishing Group UK,Nature Publishing Group
• Subject: 639/624/400/561 / 639/766/400/584 / 639/766/930/2735 / Applied and Technical Physics / Charged particles / Copper / Diffraction patterns / Electric fields / Electron acceleration / Electron beams / Electron energy / Electron guns / Electron sources / Electrons / Emittance / Image manipulation / Image quality / Microscopy / Photoexcitation / Physics / Physics and Astronomy / Quantum Physics / Single crystals / Temporal resolution / Waveguides