Ole Rømer Colloquium

Speaker:

Thomas Pfeifer

Max-Planck Institut für Kernphysik (MPIK) Heidelberg

Host:

Marcel Mudrich

Title:

 Listening to the ultrafast chat of two excited electrons

- and asking them some quick physics questions

Abstract:

Electrons interact via the Coulomb force, repel each other and feel attracted by a nucleus that normally keeps them trapped inside an atom.  When both electrons of Helium are in excited states, they keep communicating repulsively until typically one of them drops back down to the ground state, giving its energy to the other one to escape the atomic binding potential (autoionization).

Here, I will show how this very fast communication and the corresponding fundamental dynamical processes are recorded and translated into a time-domain physics language. The key methods in our experimental research are the combination of ultrafast laser/light fields (including High-Harmonic Generation and Free-Electron Lasers) and multi-dimensional measurement techniques accessing time scales of 1 femtosecond (10^-15 s) and shorter.  Moreover, we ask some correspondingly short questions encoded into visible frequencies of time- and intensity-tunable laser pulses. Listening to the electrons' optical response by extreme-ultraviolet (XUV) spectroscopy we learned to interpret a fundamental quantum interference process—the Fano resonance—in the time domain.  This understanding currently fuels several new science and technology applications ranging from laser-like coherent resonant hard-x-ray gain (but without inversion) to frequency combs locked to nuclear resonances for precision spectroscopy.

Figure: A correlated wavefunction of 2 electrons inscribed into a Fano family of curves, which can be parametrized by the traditional Fano-q parameter or a dipole-phase ? related by a simple mathematical formula.

Coffee and cake will be available from 15.05