Advance into previously unattained time spans - physicists from Kassel involved in attosecond project

To observe and understand processes at the atomic and sub-atomic level, experimental physics uses ultrashort light pulses with which atoms or molecules are bombarded in large particle accelerators. The reactions of the atoms, such as the angle at which they decay, allow conclusions to be drawn about their properties and behavior, for example how they react with other atoms. The shorter the light pulses, the better the "slow motion" with which this reaction can be observed. Since the formation process of the radiation used is random within certain limits, the properties of the individual pulses, of which hundreds to several thousands are generated per second, have so far only been very roughly known.

This limitation has now been overcome by an international collaboration of scientists. To do this, they built a so-called "atto-clock" using a measurement setup consisting of electron detectors arranged in a ring like the face of a clock. When an X-ray pulse hits an atom or molecule in the center of the ring, it shoots electrons out of it. These electrons are then hit by a circularly polarized laser, which serves as an (atto)second hand, and fly along the detector ring before "landing" on one of them. How fast and how many do so in the particular detector tells scientists the intensity, pulse duration and wavelength of the pulse used. Only then can the behavior of the atom be interpreted, such as how the individual steps of a chemical reaction take place.

Dr. Gregor Hartmann from the Institute of Physics at the University of Kassel was mainly responsible for the data analysis: ,,Besides the direct detection of the ultrashort light pulses, the greatest joy is that with our method each individual shot of the free-electron lasers can be characterized in terms of time and energy. This creates tremendous added value in each experiment of these facilities, as the respective experimenters can now finally pick out very specific radiation properties in their data analysis, which was simply not possible before."

The results have now appeared in the journal Nature Photonics and even made it to the cover of the current issue.

Link to the Nature article: https://www.nature.com/articles/s41566-018-0107-6

Download the images in high resolution: https://www.xfel.eu/news_and_events/news/index_eng.html?openDirectAnchor=1450&two_columns=0

Press release of the Stanford PULSE Institute, California, about the attosecond project: https://www6.slac.stanford.edu/news/2018-04-04-tick-tock-attoclock-tracking-x-ray-laser-pulses-record-speeds.aspx

Contact:
Dr. Gregor Hartmann
University of Kassel
Department of Experimental Physics IV/ Thin Films & Synchrotron Radiation
Tel: +49 561 804-4354
E-mail: gregor.hartmann[at]physik.uni-kassel[dot]de
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