Compact single-shot electro-optic detection system for THz pulses with femtosecond time resolution at MHz repetition rates

Electro-optical detection has proven to be a valuable technique to study temporal profiles of THz pulses with pulse durations down to femtoseconds. The Coulomb field of a relativistic electron bunch resembles the current profile, and therefore electro-optical detection can be exploited for non-invasive bunch length measurements at accelerators. Here we present a compact and robust electro-optical detection system based on spectral decoding to measure single-shot longitudinal bunch profiles of electron bunches down to 200 fs. Apart from the GaP crystal and the corresponding laser optics at the electron beamline all components are housed in 19-inch chassis for rack mount and remote operation inside the accelerator tunnel. The novel linear photo diode array KALYPSO [1] allows to acquire the modulated laser spectra at frame rates of up to 2.26 MHz. First longitudinal bunch profile measurements at the European X-ray Free Electron Laser (XFEL) show bunch length of around 400 fs (rms) with an arrival-time jitter of 35 fs (rms).