Acceleration and manipulation of electron bunches underlie most electron and X-ray devices used for ultrafast imaging and spectroscopy. New terahertz-driven concepts offer orders-of-magnitude improvements in field strengths, field gradients, laser synchronization and compactness relative to conventional radio-frequency devices, enabling shorter electron bunches and higher resolution with less infrastructure while maintaining high charge capacities (pC), repetition rates (kHz) and stability. We present a segmented terahertz electron accelerator and manipulator (STEAM) capable of performing multiple high-field operations on the 6D-phase-space of ultrashort electron bunches. With this single device, powered by few-micro-Joule, single-cycle, 0.3 THz pulses, we demonstrate record THz-acceleration of >30 keV, streaking with <10 fs resolution, focusing with >2 kT/m strength, compression to ~100 fs as well as real-time switching between these modes of operation. The STEAM device demonstrates the feasibility of THz-based electron accelerators, manipulators and diagnostic tools enabling science beyond current resolution frontiers with transformative impact.

Photoinduced bonding instability of IrTe2 studied with ultrafast electron diffraction and density functional theory.

Terahertz-based electron acceleration has recently emerged as a promising candidate for driving next-generation highbrightness electron sources. Although initial demonstrations have proven the feasibility of this technology for accelerating and manipulating the phase space of electrons, further demonstrations of exquisite timing control are required to make use of terahertz acceleration for demanding applications such as light sources and ultrafast electron diffraction. In this paper, we use a two-stage segmented-terahertz-electron-accelerator-and-manipulator (STEAM) setup to demonstrate control over the electron beam energy, energy spread, and emittance. The first rebunching stage is used to tune the duration of 55 keV electron bunches from a DC electron gun that enables femtosecond phase control at the second accelerating stage. For optimized parameters, energy spread and emittance are reduced by 4× and 6×, respectively, relative to operation with the first stage off. A record energy gain of ∼70 keV was achieved at a peak accelerating field of 200 MV/m, resulting in a >100% energy boost in a terahertz-powered accelerator for the first time. These results represent a critical step forward for the practical implementation of terahertz-powered devices in ultrafast electron sources.

Terahertz (THz)-based electron acceleration and manipulation has recently been shown to be feasible and to hold tremendous promise as a technology for the development of next-generation, compact electron sources. Previous work has concentrated on structures powered transversely by short, single-cycle THz pulses, with mm-scale, segmented interaction regions that are ideal for acceleration of electrons in the sub-to few-MeV range where electron velocities vary significantly. However, in order to extend this technology to the multi-MeV range, investigation of approaches supporting longer interaction lengths is needed. Here, we demonstrate first steps in electron acceleration and manipulation using dielectrically-lined waveguides powered by temporally long, narrowband, multi-cycle THz pulses that co-propagate with the electrons. This geometry offers centimeter-scale single-stage interaction lengths and offers the opportunity to further increase interaction lengths by cascading acceleration stages that recycle the THz energy and rephase the interaction. We prove the feasibility of THz-energy recycling for the first time by demonstrating acceleration, compression and focusing in two sequential Al 2 O 3 -based dielectric capillary stages powered by the same multi-cycle THz pulse.Since the multi-cycle energy achievable using laser-based sources is currently a limiting factor for the maximum electron acceleration, THz energy recycling provides a key enabling factor for reaching relativistic energies with existing sources.