Measurement of low-energy and low-charge ultrashort bunches using an S-band RF deflector

Ultrafast Electron Diffraction (UED) system, using an electron bunch of the duration with less than 100 fs and of the energy with 3 MeV, has been developed as a tool probing the ultrafast dynamics in pump–probe experiments. To keep the temporal and transverse characteristics of the electron bunch for the time-resolved electron diffraction, the bunch charge is limited to be the pico-Coulomb or less. S-band transverse deflecting cavity working on TM120 mode is designed, fabricated, and installed in the UED system to measure directly the fs-scaled pulse duration of low-energy and low-charge electron bunches. We describe the design and the expected performance of a single-cell RF deflector. For the electron beam of 3 MeV in energy and 1.88 pC in charge, we could measure the bunch duration of 69 fs and the timing jitter of 62 fs, both in rms.