First megahertz rate timing jitter observed

A report published today in the Journal Optica demonstrates accurate synchronisation of optical and X-ray lasers crucial for pump-probe experiments at XFEL. These snapshots taken during a reaction are stitched together to make molecular movies.

One of the ultimate goals for scientists using state-of-the-art X-ray free-electron lasers such as European XFEL is to be able to film the details of chemical and biological reactions. By stitching together a series of snapshots taken at different time intervals during a reaction, a molecular movie can be made of the process. So called pump-probe experiments use a precisely synchronised optical laser to trigger a reaction (the ‘pump’), while the X-ray laser takes a snapshot of the molecular structure at defined times during the reaction (the ‘probe’).

European XFEL now generates the ultrafast and ultra-intense light pulses needed to capture these processes that occur on extremely short timescales. The pulses of X-ray light generated by European XFEL are each less than a few millionths of a billionth of a second, or a few femtoseconds – fast enough to capture the series of events in a biological or chemical reaction. An accurate synchronization of the X-ray and optical laser pulses at these timescales is, however, challenging. Furthermore, tiny variations in the alignment and path travelled by the laser pulses caused, for example, by fluctuations in air pressure, or expansion in the electrical cables, have a relatively large impact on the accuracy of this experimental set-up. This variation is known as ‘timing jitter’. For pump-probe experiments to be successful, the jitter must be kept to a minimum, and be accurately characterized so that scientists can take it into account when assessing their data.

Read more on the European XFEL website

Image : The XPB/SFX instrument at European XFEL.

Credit: European XFEL / Jan Hosan