Laser arrival time measurement and correction for the SwissFEL lasers

To probe ultrafast processes at SwissFEL it is crucial that the pump laser, used at the end stations, arrives in time with the generated X-ray pulses. For fs resolution pump probe experiments a path-length change of few-hundred nanometers already affects the measurement quality. The length of SwissFEL and the total propagation path of the pump laser light to the experiment is in the scale of several hundred meters, which makes this task challenging. The Timing and Synchronization and the SwissFEL laser group are working on developing tools to measure and correct the timing over the machine complex. They report on the Laser Arrival Monitor (LAM) concept for the SwissFEL gun laser, which produces the electron bunch at the start of the linear accelerator (1). This device is based on high bandwidth electro-optical modulators adapted from telecommunication. They also report on the first results using a spectrally resolved cross-correlator, which enables to measure time of arrival with fs resolution and to correct long term timing drifts of a Terrawatt class Ti:sapphire laser system from the ps level to below 10 fs over 10 hours. The measurements will also help to identify the major sources of drift for passive stabilization. These results are important to enable fs resolution pump-probe experiments at SwissFEL. Notes

1: Marta Csatari Divall; Albert Romann; Patrick Mutter; Stephan Hunziker; Christoph P. Hauri, "Laser arrival measurement tools for SwissFEL", Proc. SPIE 9512, Advances in X-ray Free-Electron Lasers Instrumentation III, 95121T (May 12, 2015); 10.1117/12.2179016