Intensity and timing jitter compensated ultra-fast experiments at accelerator-driven photonsources
Timing jitter and power instabilities are crucial parameters which greatly reduce the applicability of accelerator driven light sources for time-resolved experiments. In this contribution we present a technique that allows achieving few 10 fs time-resolution in experiments operating at cw repetition rates of up to 100 kHz at presents of timing jitter in order of ps. As we show on the example of a benchmark experiment based on THz driven magnetization dynamics, our method provides a sensitivity or dynamic range that is comparable to all-laser based techniques. Moreover we show how the time and power instabilities in combination with a high repetition rate can be turned from a problem into a favor an advantage and can be utilized as an ultrafast delay line and attenuator. Our method employs a fs-level arrival time monitor based on electro-optic sampling of residual pulses from a coherent diffraction radiatior and a fast THz detector allowing for pulse to pulse detection of arrival time and pump pulse intensity. The monitor can operate at high repetition rates (presently up to a few 100 kHz) and low electron bunch charges (sub pC). The prototype device has been tested at the quasi CW linear RF electron accelerator (ELBE). Despite timing jitter of 1.5 ps (FWHM) and 15% intensity fluctuations of the pump pulse intensity, a temporal resolution of around 20 fs (peak-to-peak) and a dynamic range of 100 dB was achieved. Our method has high potential to provide few fs level synchronization on next generation large scale X-ray photon sources based on high repetition rate electron accelerators such as LCLSII. A demonstrator aiming at operation up to 4.7 MHz is under development for the European X-FEL within the frame of a recently granted EU project within the HORIZON2020 program.