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

Abstract

Electro-optical detection has proven to be a valuable technique to study temporal profiles of THz pulses with pulse durations down to femtoseconds. As the Coulomb field around a relativistic electron bunch resembles the current profile, electro-optical detection can be exploited for non-invasive bunch length measurements at accelerators. We have developed a very compact and robust electro-optical detection system based on spectral decoding for single-shot longitudinal bunch profile monitoring at the European X-ray free electron laser (XFEL) for electron bunch lengths down to 200 fs (rms). Apart from the GaP crystal and the corresponding laser optics at the electron beamline, all components are housed in 19 " chassis for rack mount and remote operation inside the accelerator tunnel. An advanced laser synchronization scheme based on radio-frequency down-conversion has been developed for locking a custom-made Yb-fiber laser to the radio-frequency of the European XFEL accelerator. In order to cope with the high bunch repetition rate of the superconducting accelerator, a novel linear array detector has been employed for spectral measurements of the Yb-fiber laser pulses at frame rates of up to 2.26 MHz. In this paper, we describe all sub-systems of the electrooptical detection system as well as the measurement procedure in detail, and discuss first measurement results of longitudinal bunch profiles of around 400 fs (rms) with an arrival-time jitter of 35 fs (rms).

Phase Diversity Electro-optic Sampling: A new approach to single-shot terahertz waveform recording

“…The emitted photon pulses depend directly on the properties of the electron bunches. Hence the diagnostics of their longitudinal shape has been the subject of an intense research in the last years 22 , 31 – 34 .…”

“…Details of laser transport and KALYPSO focusing optics are not shown—see ref. 34 for further details …”

Real-Time Data Acquisition and Processing System for MHz Repetition Rate Image Sensors

“…The horizontal axis has several interpretations: it corresponds to the light position on the detector, which maps to the wavelength and to the time delay from the laser pulse. More detailed verification of the EOD operation is presented in a separate paper [4].…”

“…Analysis of data captured in the EuXFEL is provided in a separate publication [4]. Evaluation of the KALYPSO detector is provided in the papers [11,17].…”

“…It uses an electro-optic crystal, located around 6 mm from the beam path, to encode the beam charge density profile on the spectrum of an IR laser pulse (1050 µm). The longitudinal charge distribution is then reconstructed using data from a fast spectrometer [4].…”