Quantitative Untersuchung der Multi-Photon-Ionisation von Edelgas- und Metallatomen mit Freie-Elektronen-Laser-Strahlung in weichen Röntgengebieten

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At the new Free-Electron Laser (FEL) FLASH (Free-Electron LASer in Hamburg) at DESY for soft X-rays of ultra-high intensity, photoionization of rare gases and free open-shell metal atoms will be studied by means of ion and electron spectroscopy. Of particular interest are non-linear effects such as sequential, direct, and resonant multi-photon ionization processes and strong-field phenomena as well, investigated at photon energies above atomic ionization thresholds. Our aim is a better understanding of the interaction between ionizing electromagnetic radiation of ultra-high intensity and matter in general and, in particular, the influence of electron correlation. Specific aspect of the experiments proposed is their quantitative character by absolute determination of photon number, spot size, pulse duration and, hence, FEL irradiance using a calibrated set-up. The measurements require a focused soft X-ray FEL beam to achieve irradiance values up to 1017 W cm-2. FLASH is currently the only place in the world where those experiments may be performed.