Record time resolution


After being illuminated with light, the atoms in materials react within femtoseconds, i.e. quadrillionths of a second. To observe these reactions in real time, the experiment setup used to capture them must operate with femtosecond time resolution too, otherwise the resulting images will be “blurred”. In a proof-of-principle experiment at the European XFEL, a research team has demonstrated a record time resolution of around 15 femtoseconds—the best resolution reported so far in a pump–probe experiment at an X-ray free-electron laser (FEL) facility, while keeping a high spectral resolution. “These results open up the possibility of doing time-resolved experiments with unprecedented time resolution, enabling the observation of ultrafast processes in materials that were not accessible before,” explains Daniel Rivas from European XFEL, principal investigator of the experiment and first author of the publication in the scientific journal Optica, in which the team from European XFEL and the DESY research centre in Hamburg report their results.

One of the goals of experiments at the European XFEL is to record “molecular movies”, i.e. series of snapshots of dynamic processes taken in extremely rapid succession, which reveal the details of chemical reactions or physical changes in materials at high time resolution. Understanding the molecular rearrangement during such reactions is an essential step towards controlling processes in our natural environment, such as radiation damage in biological systems or photochemical and catalytic reactions. One technique to create such movies is pump–probe spectroscopy, where an optical laser pulse (the “pump” pulse) excites a certain process in a sample and the X-ray laser pulses (the “probe” pulses) are used to take a series of snapshots in order to observe how the process evolves in time.

Read more on the European XFEL website

Image: An ultrashort X-ray pulse and an optical laser pulse interact simultaneously with a neon atom. The X-ray pulse removes an electron from the inner electronic shell and, due to the electromagnetic field of the optical laser that is present at the moment of ionization, the outcoming electron is modulated in energy.

Credit: in cooperation with European XFEL