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.
Highlights
The central challenge of an electron gun is to accelerate electrons from rest to high energies as quickly as possible to avoid the beam-degrading effects of space charge, which scale inversely as the electron energy squared [1] or as the extraction field squared
The potential advantages of photonic linacs have not extended to photonic guns, the initial acceleration stage that is quintessential to determining the final electron beam quality and can benefit most from higher accelerating fields
Our first results demonstrate high field (350 MV/m) acceleration up to 0.8 keV, as well as percent-level energy spread in sub-kiloelecton volt, several tens of fC bunches
Summary
The central challenge of an electron gun is to accelerate electrons from rest to high energies as quickly as possible to avoid the beam-degrading effects of space charge, which scale inversely as the electron energy squared [1] or as the extraction field squared. Our first results demonstrate high field (350 MV/m) acceleration up to 0.8 keV, as well as percent-level energy spread in sub-kiloelecton volt, several tens of fC bunches.
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