Electro-Optic Technique with Improved Time Resolution for Real-Time, Nondestructive, Single-Shot Measurements of Femtosecond Electron Bunch Profiles

Electro-optic detection of the Coulomb field of a relativistic electron bunch combined with single-shot cross correlation of optical pulses is used to enable single-shot measurements of the shape and length of femtosecond electron bunches. This method overcomes a fundamental time-resolution limit of previous single-shot electro-optic measurements, which arises from the inseparability of time and frequency properties of the probing optical pulse. Using this new technique we have made real-time measurements of a 50 MeV electron bunch, observing the profile of 650 fs FWHM ($\sim 275\mathrm{f}\mathrm{s}$ rms) long bunches.

Figure 1

Experimental setup for measuring single-shot images of the longitudinal electric field profiles of individual electron bunches.

Figure 2

Electro-optic detection of the electric field profile of a single electron bunch using the temporal decoding method (solid curve) and the spectral decoding method [short-dashed (blue) line]. The leading edge of the bunch is on the left. The long-dashed (red) curve shows a simulation of the spectral decoding trace obtained by convoluting the temporal decoding trace using Eq. (1).

Figure 3

The electro-optic signal (a) and electric field profile (b) of the same electron bunch. The inset shows a sequence of single-shot measurements, indicating that the timing jitter is of the same order of magnitude as the bunch duration.

Figure 4

Single-shot measurements of individual electron bunches for different settings of the phases of the bunchers and accelerator sections.