Fully differential studies for two-photon non-sequential double ionization of helium using a reaction microscope at FLASH

点击翻译按钮获取中文摘要

Two-photon induced double ionization (TP-DI) of helium is of decisive and fundamental importance to advance non-linear theories and explore electron-electron correlations, particularly for non-sequential ionization. Using the free electron laser (FEL) at Hamburg (FLASH), the only fourth generation radiation source operational world wide, delivering unprecedented intensities (~1013-1016 W/cm2) at ultra-short pulse durations (~30 fs and less) in combination with the most advanced multi-particle detection system - the Heidelberg reaction microscope - we studied for the first time He2+ recoil-ion momentum distributions (RIMD) at a photon energy of 44 eV, one of the goals of the previous proposal. The results represent evidence for preferential back-to-back emission of two electrons with almost equal energy sharing, which unambiguously distinguishes it from sequential ionization of Ne observed at 44 eV by our fully differential measurements. However, the present RIMD can not finally benchmark significant deviations in differential as well as total cross sections between the predictions of different recent advanced calculations and, therefore, fully differential measurements for direct TP-DI of He are highly demanded, an ultimate aim of this proposal. These studies are indispensable for the understanding of more complex situations when FEL-radiation interacts with many-electron atoms, molecules, clusters, surfaces or bulk-matter in the extreme ultraviolet regime.