Terahertz-driven, all-optical electron gun

TL;DR

This paper introduces a novel all-optical terahertz-driven electron gun that produces ultrashort, high-quality electron beams with potential applications in time-resolved electron diffraction and low-energy electron microscopy.

Contribution

It demonstrates a new micron-scale THz gun capable of generating near 1 keV electrons with high acceleration fields and synchronized, quasimonoenergetic bunches, improving upon conventional RF guns.

Findings

Achieved peak electron energies approaching 1 keV.

Generated sub-keV, quasimonoenergetic electron bunches with 32 fC charge.

Provided a practical, compact, and synchronized electron source for advanced experiments.

Abstract

Ultrashort electron beams with narrow energy spread, high charge, and low jitter are essential for resolving phase transitions in metals, semiconductors, and molecular crystals. These semirelativistic beams, produced by phototriggered electron guns, are also injected into accelerators for x-ray light sources. The achievable resolution of these time-resolved electron diffraction or x-ray experiments has been hindered by surface field and timing jitter limitations in conventional RF guns, which thus far are <200 MV/m and >96 fs, respectively. A gun driven by optically-generated single-cycle THz pulses provides a practical solution to enable not only GV/m surface fields but also absolute timing stability, since the pulses are generated by the same laser as the phototrigger. Here, we demonstrate an all-optical THz gun yielding peak electron energies approaching 1 keV, accelerated by 300 MV/m THz fields in a novel micron-scale waveguide structure. We also achieve quasimonoenergetic, sub-keV bunches with 32 fC of charge, which can already be used for time-resolved low-energy electron diffraction. Such ultracompact, easy to implement guns driven by intrinsically synchronized THz pulses that are pumped by an amplified arm of the already present photoinjector laser provide a new tool with potential to transform accelerator based science.