Stuttgart 2012 – wissenschaftliches Programm

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A: Fachverband Atomphysik

A 12: Interaction with strong or short laser pulses III

A 12.1: Hauptvortrag

Dienstag, 13. März 2012, 10:30–11:00, V47.03

Two-color photoionization studies at XUV and X-ray Free Electron Lasers — •Michael Meyer — European XFEL GmbH, Albert-Einstein-Ring 19, D-22761 Hamburg, Germany

The combination of intense femtosecond X-ray and NIR pulses produced by Free Electron Lasers (FEL) and synchronized optical lasers, respectively, offers various new opportunities to investigate the dynamics of atomic photoionization. Some recent results obtained at the XUV-FEL FLASH in Hamburg and the first X-ray FEL, the LCLS in Stanford, will be presented. In the experiments at FLASH, the optical dressing field gives rise to the so-called two-color Above Threshold Ionization, which could be studied for the first time in a regime free from unwanted interference effects. For resonant excitations, e.g. 3d --> 5p in atomic Kr, the NIR field causes a strong modification of the decay dynamics, which was experimentally investigated via the intensity-dependent shift of the resonance position and via the competition between resonant and direct Auger processes. Recent experiments at LCLS have taken advantage of the very short (2-5 fs) pulse duration, which coincides with the lifetime of the Ne 1s core hole and with the temporal width of one optical cycle of the NIR (800 nm) dressing laser. As a direct consequence, the angle-resolved KLL Auger spectra reveal strong intensity modulations induced by sub-cycle interferences, i.e. by the coherent emission of electrons produced during one cycle of the superimposed optical field.