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

在DESY新研制的用于超高强度软x射线的自由电子激光器（FEL） FLASH （free - electron Laser in Hamburg, free - electron Laser in Hamburg）上，将利用离子能谱和电子能谱研究稀有气体和自由开壳金属原子的光离。特别感兴趣的是非线性效应，如顺序，直接和共振多光子电离过程和强场现象，以及在光子能量高于原子电离阈值时的研究。我们的目的是更好地理解超高强度电离电磁辐射与一般物质之间的相互作用，特别是电子相关的影响。提出的实验的具体方面是它们的定量特征，通过绝对确定光子数，光斑大小，脉冲持续时间，因此，使用校准装置的FEL辐照度。测量需要聚焦软x射线自由电子束流来实现高达1017 W cm-2的辐照度值。FLASH是目前世界上唯一可以进行这些实验的地方。

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.