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

We propose and demonstrate a method to reduce the pulse width and timing jitter of a relativistic electron beam through THz driven beam compression. In this method the longitudinal phase space of a relativistic electron beam is manipulated by a linearly polarized THz pulse copropagating in a dielectric tube such that the bunch tail has a higher velocity than the bunch head, which allows simultaneous reduction of both pulse width and timing jitter after passing through a drift. In this experiment, the beam is compressed by more than a factor of 4 from 130 fs to 28 fs with the arrival time jitter also reduced from 97 fs to 36 fs, opening up new opportunities in using pulsed electron beams for studies of ultrafast dynamics. This technique provides an effective way to manipulate beam longitudinal phase space with a THz pulse and may have a strong impact in accelerator and ultrafast science facilities that require femtosecond electron beams with tight synchronization to external lasers.

Figure 1

THz driven relativistic electron beam compression experiment setup. The 3.0 MeV electron beam is compressed by the first THz pulse with vertical polarization and measured by the second THz pulse with horizontal polarization. The THz pulses are focused to the dielectric tubes ($D1$ and $D2$) with off-axis parabolic mirrors (OAP) in colinear configurations.

Figure 2

Beam distributions at screen $P2$ (a) and longitudinal and transverse energy kicks (b) for various offsets in $D1$. The superimposed beam distribution on $P2$ for a fine scan of offsets in $D1$ is shown in (c).

Figure 3

Longitudinal and transverse energy kicks as a function of time delay between the first THz pulse and electron beam.

Figure 4

Beam distributions at screen $P1$ measured with both THz pulses on for various time delays between the first THz pulse and the electron beam. (a)–(d) correspond to the cases when the electron beam is at regions $A$, $B$, $C$, and $D$ in Fig. 2.

Figure 5

50 consecutive single-shot measurements of the beam temporal profile without (a) and with (d) the THz buncher, and the rms pulse width statistics collected over 500 consecutive shots without (b) and with (e) the THz buncher. The beam centroid for each individual shot (black dots) is used to determine the time jitter without (c) and with (f) the THz buncher.