Resonant two-photon ionisation of helium measured with angular resolution
Using a new experimental method, physicists from the Max Planck Institute for Nuclear Physics in Heidelberg investigated the resonant two-photon ionisation of helium with improved spectral resolution and angular resolution. For this purpose, they utilised a reaction microscope in combination with a high-resolution extreme-ultraviolet (EUV) photon spectrometer developed at the Institute. The measurements have been performed at the Free Electron Laser in Hamburg (FLASH), a brilliant radiation source, delivering intense EUV laser flashes. This allows the events from each individual laser flash to be analysed in terms of photon energy, yielding spectrally high-resolution data sets.
Helium, as the simplest and most accessible multi-electron system, is ideally suited for fundamental theoretical and experimental studies. Here, the mutual electrical repulsion of the two electrons plays an essential role – it accounts for a good third of the total binding energy. Of particular and fundamental interest is the interaction with photons (the quanta of light). Researchers from the groups around Christian Ott and Robert Moshammer in the division of Thomas Pfeifer at the Max Planck Institute for Nuclear Physics in Heidelberg have investigated the resonant two-photon ionisation of helium in detail at the free-electron laser FLASH of DESY in Hamburg.
Read more on the DESY website
Image: Fig. 2: Spectrum of photons unsorted (top) and sorted by peak position (bottom).