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.