Evidence for Chirped Auger-electron Emission


If a high-energy photon liberates an inner-shell electron from an atom, a photoelectron and a core vacancy are created. The latter is subject to decay, which produces Auger electrons with charateristic energies. For cases in which the Auger electron is faster, it may overtake the preceding photoelectron. Due to the altered screening of the ion's charge, the result is an exchange of energy between both electrons. This effect is known as post-collision interaction and happens during 0.1 to 100 fs after the photoionization. Now, the first observation of this overtaking process in the time domain was achieved by experimentalists from Hamburg University and DESY, led by Markus Drescher. To achieve this, femtosecond XUV pulses from FLASH were combined with a THz streak camera in a pump-probe fashion. The Auger-electron energy spectra were interpreted by Sebastian Bauch, PhD student at the chair of Michael Bonitz (ITAP), utilizing quantum and classical simulations as well as an analytical line shape model. The results are published in Physical Review Letters.
Press releases of the CAU and Hasylab


The figure shows the comparison of the measured and the calculated Auger-electron spectra for different pump-probe time delays. The overtaking process manifests itself in different linewidths for rising and falling slope of the vector potential (center and lower panel).