Cascaded Multicycle Terahertz-Driven Ultrafast Electron Acceleration and Manipulation

Abstract

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.

THz-Enhanced DC Ultrafast Electron Diffractometer

“…Electron Bunch Compression. For electron bunch compression, we have chosen the DLW structure powered with a long multicycle THz pulse [18], which provides a more homogeneous field distribution and larger effective area compared to the solutions based on the single-cycle THz pulses [16,17]. The cylindrical waveguide supports a travelling transverse-magnetic waveguide mode (TM 01 mode).…”

“…The DLW, which can be used for multiple THz-based electron manipulations, supports a TM 01 mode whose transverse field distribution is shown in Figure 2(a). For the longitudinal waveform, there are four key phase points to note [18]: the positive and negative crests of the waves, where the field gradient is minimized, and the positive and negative "zero crossings" of the field, where the field gradient is maximized. The positive and negative crests correspond to deceleration and acceleration of the electron bunch, respectively, but leave the bunch spatial and temporal dimensions unchanged.…”

“…It has been recently shown that laser-based terahertz (THz) radiation-powered electron acceleration and manipulation provides a promising solution for construction of future ultrafast electron sources that support high energy, high repetition rate short electron bunches while being compact [16][17][18][19][20]. At millimeter-scale wavelengths, THz radiation has been proven to enable GV/m field strength [21], which is well-suited for subpicosecond electron beam manipulation.…”

“…At millimeter-scale wavelengths, THz radiation has been proven to enable GV/m field strength [21], which is well-suited for subpicosecond electron beam manipulation. THz-driven electron manipulation can also be used to compress electron bunches to sub-100 fs duration without intrinsic timing jitter [16][17][18][19][20]. By combining the THz-based compressor with a conventional TEM, Ryabov and Baum [22] have compressed electrons to about 80 fs with~10 electrons/pulse and demonstrated its application in probing the electromagnetic field induced by the excitation laser on the sample.…”

Focusing Waveguide Structure for High-Gradient Electron Acceleration by Picosecond Terahertz Pulses

“…To increase the energy gain, a long accelerating structure is required. Two possible approaches for the design of such structures have been demonstrated in a series of papers [21][22][23]. In them, an ultrashort terahertz pulse was either launched into a dielectric capillary along the accelerated beam [21] or fed a metal accelerating structure consisting of several cells next to it [22,23].…”