Terahertz-based subfemtosecond metrology of relativistic electron beams

We demonstrate single-shot temporal characterization of relativistic electron bunches using single-cycle terahertz (THz) field streaking. A transverse deflecting structure consisting of a metal slit enables efficient coupling of the THz field and electron bunch. The intrinsically stable carrier envelope phase and strong gradient of the THz pulses allow simultaneous, self-calibrated determination of the time-of-arrival with subfemtosecond precision and bunch duration with single-femtosecond precision, respectively, opening up new opportunities for ultrafast electron diffraction as well as accelerator technologies in general.

Figure 1

Schematic of the experimental configuration.

Figure 2

Experimental data of electron bunch time-of-arrival measurements by THz streaking. (a)–(d) show raw images of streaked electron bunches at different time delays, indicated by dashed lines in (e) showing the beam centroid versus time delay. The scale bars in (a)–(d) correspond to 1.0 mm on the detector screen or 0.31 mrad in divergence. (f) Pointing stability of the electron beam when the THz is off.

Figure 3

Experimental data of the relative-to-laser time jitter and the bunch length of the electron beams determined from single-shot THz streaking images. From (a)–(c) the comparison of single-shot electron beams profiles with the THz off and on, one can determine the relative time-of-arrival [vertical arrow in (c)] and bunch length [horizontal arrow in (c)] of every electron pulse. (a)–(c) have same horizontal axes. The scale bars in (a) and (b) correspond to 1.0 mm on the detector screen or 0.31 mrad in divergence. (d)–(e) show the time-of-arrival of 1000 electron shots. After removing the slow timing drift, the timing stability is 45.8 fs rms. (f)–(g) show the bunch length for the same 1000 shots after deconvolution. The bunch length is $21.3\pm 1.3\mathrm{fs}\mathrm{rms}$.

Figure 4

Simulation results of angular position, integrated transverse voltage, and Lorentz forces experienced by the relativistic electrons. (a) Comparison between the measured and simulated final angular position of the electrons at different time delays. (b)–(f) compare the kinetics of two particles highlighted in (a): “max. $\mathrm{\Delta }{y}^{\prime }$” with the maximum change in angular position and “zero $\mathrm{\Delta }{y}^{\prime }$” with the angular motion integrated to zero. The two dashed vertical lines indicate the slit. (b) compares the integrated transverse voltage experienced by the two particles. (c)–(d) show the components and combined Lorentz force experienced by the “max. $\mathrm{\Delta }{y}^{\prime }$” particle. (e)–(f) show the components and combined Lorentz force experienced by the “zero $\mathrm{\Delta }{y}^{\prime }$” particle.