Terahertz Oscilloscope for Recording Time Information of Ultrashort Electron Beams

Abstract

We propose and demonstrate a Terahertz (THz) oscilloscope for recording time information of an ultrashort electron beam. By injecting a laser-driven THz pulse with circular polarization into a dielectric tube, the electron beam is swept helically such that the time information is uniformly encoded into the angular distribution that allows one to characterize both the temporal profile and timing jitter of an electron beam. The dynamic range of the measurement in such a configuration is significantly increased compared to deflection with a linearly polarized THz pulse. With this THz oscilloscope, nearly 50-fold longitudinal compression of a relativistic electron beam to about 15 fs (rms) is directly visualized with its arrival time determined with 3 fs accuracy. This technique bridges the gap between streaking of photoelectrons with optical lasers and deflection of relativistic electron beams with radio-frequency deflectors, and should have wide applications in many ultrashort electron beam based facilities.The ability to characterize the time information of an ultrashort electron beam including both the temporal profile and arrival time is crucial for optimizing and enhancing the performance of many electron beam based scientific facilities such as free-electron lasers (FELs [1-3]), ultrafast electron diffraction (UED [4,5]) and microscopy (UEM [6-9]), laser-driven and beam-driven advanced accelerators [10-15], etc. In accelerator community, radio-frequency (rf) deflecting cavities have been widely used to measure the temporal profile of relativistic electron beams with energy ranging from MeV to GeV (see, e.g. [16][17][18]). However, the information of beam arrival time with respect to an external laser as required in a pump-probe experiment can not be directly measured with an rf deflector. In attosecond science community, streaking of photoelectrons with optical lasers has become a standard technique for characterizing the complete information of attosecond pulses [19]. Recently, this technique has been adapted to characterize femtosecond x-ray pulses in FELs with the streaking imprinted by farinfrared and THz pulses [20][21][22][23]. However, this technique doesn't apply to a relativistic electron beam, as dictated by Lawson-Woodward theorem [24]. Very recently, THz streaking of keV and MeV electrons [25][26][27] in a sub-wavelength metallic structure has been used to measure both the temporal profile and arrival time of electron beams. However, the small aperture used to enhance THz field may significantly limit the number of useful electrons. Furthermore, with the streaking imprinted by a linearly polarized THz pulse, the beam receives sinusoidal angular streaking and thus the measurement has a rather limited dynamic range (time window where the measurement is accurate) comparable to about one quarter of the wavelength.In this Letter, we demonstrate a laser-driven THz oscilloscope that allows one to record the complete time information of an ultrashort electron beam with both large dynamic range and high tem...

Terahertz strong-field physics in light-emitting diodes for terahertz detection and imaging

“…This is fueled by the impressive advancements made during the last two decades in the development of femtosecond laser-based table-top sources for strong THz radiation [11][12][13] . These intense THz electromagnetic fields have been utilized [14][15][16][17][18] to efficiently accelerate and manipulate electrons to extreme degrees, advancing the frontiers of both the technology and science of nonlinear THz-matter interactions. For example, acceleration of relativistic electron bunches in free space is promising for the realization of next-generation table-top particle accelerators and compact X-ray sources.…”

Femtosecond Relativistic Electron Beam with Reduced Timing Jitter from THz Driven Beam Compression

“…In our experiment, a vertically polarized THz pulse is directly injected into a dielectric tube (D1) and thus only HEM11 mode is excited. Such a mode has recently been used to deflect electron beam for measuring bunch length and timing jitter [26]. It should be noted that HEM11 mode has longitu-dinal electric field which varies linearly with transverse offset.…”

“…To allow unambiguous determination of the bunch compression effect, in our experiment a polarization rotation (PR) element consisting of a pair of wire grid polarizers and roof mirrors are used to manipulate the THz polarization. As shown in [26], by changing the path length of the two roof mirrors, a vertically polarized THz pulse can be converted into a horizontally polarized pulse.…”

Parallel-plate waveguides for terahertz-driven MeV electron bunch compression

“…A promising approach for enhancing timing resolution in UED pump-probe experiments is to manipulate the electron beam using THz electromagnetic radiation intrinsically synchronized with pump lasers prior to sample interaction. Previously, experimental work was done to demonstrate attosecond electron diagnostics using laser-generated singlecycle THz pulses [24][25][26]. This technique offers beam-to-laser timing characterization with the potential to achieve subfemtosecond accuracy, and at the same time a direct measurement of the bunch length with a sub-femtosecond resolution.…”