Tracking attosecond wave packets with extreme ultraviolet pulses

The fastest dynamical process in atoms, molecules and complexes is the electronic motion. It occurs on time scales reaching down to the attosecond regime (1 as = 10-18 s).  The advent of novel light sources, providing extreme ultraviolet (XUV) or even X-ray pulses with as pulse duration paves the way to study these dynamics in real-time. Therefore, researchers around the world are currently developing new spectroscopic techniques using pulses of XUV or X-ray radiation.

An international research collaboration from Germany, Italy, Sweden, Switzerland, Denmark and the local team at the FERMI free-electron laser, has succeeded in observing the ultrafast electronic wave-packet evolution induced by the coherent excitation of an electron out of an inner shell in argon atoms. The measured quantum interference pattern exhibits oscillations that have a period of only ≈ 150 as. In order to achieve this, the collaboration extended a spectroscopy technique known from the visible spectral range – coherent wave-packet interferometry – to the XUV regime. This required a so far unprecedented level of control over the phase and timing properties of free-electron laser pulse pairs, which was achieved by exploiting the coherence of the high-gain harmonic generation process at FERMI. This novel spectroscopy technique will provide substantial insights and real-time information about intra and inter particle decay mechanisms in the XUV range.

Read more on the Elettra website

Image: Artistic rendering of the electronic motion in the electronic shell of an atom, induced and probed by a double pulse sequence.