Hannover 2016 – scientific programme

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A: Fachverband Atomphysik

A 22: Interaction with VUV and X-ray light

A 22.17: Poster

Tuesday, March 1, 2016, 16:30–19:00, Empore Lichthof

IR-assisted XUV Multiphoton Ionization of Noble Gases at FLASH — •Georg Schmid¹, Kirsten Schnorr¹, Sven Augustin¹, Severin Meister¹, Hannes Lindenblatt¹, Defu Luo¹, Patrick Paluch¹, Lutz Fechner¹, Thomas Ding¹, Yifan Liu¹, Rolf Treusch², Stefan Düsterer², Harald Redlin², Christian Ott³, Kamal P. Singh⁴, Mathieu Gisselbrecht⁵, Claus-Dieter Schröter¹, Thomas Pfeifer¹, and Robert Moshammer¹ — ¹Max-Planck-Institut für Kernphysik, Heidelberg, Germany — ²DESY, Hamburg, Germany — ³UC Berkely, USA — ⁴IISER, Mohali, India — ⁵Lund University, Sweden

IR-XUV pump-probe experiments on atomic noble gases were performed at the free-electron laser in Hamburg (FLASH). Using a reaction microscope, we were able to measure photoions and -electrons as a function of the delay between intense IR (∼ 10¹⁴ W/cm²) and XUV pulses. For delay values with IR being present, an enhancement in the yield of Ar ions produced by multiple absorption of 27 eV photons is observed up to high ionic charge states (Ar⁵⁺). The increase is especially pronounced in the Ar²⁺ channel. Sequential absorption of two XUV photons excites Ar^+* (3s²3p⁴(¹D)3d) states which are further ionized by the IR pulse to Ar²⁺. The ion yield dependence on the XUV and IR intensity is investigated and different IR-assisted XUV multiphoton ionization pathways are distinguished. Our findings show how XUV multiphoton ionization can be controlled by IR laser pulses. For Helium at 24 eV, differences in the He⁺ photoion and -electron momentum distributions are observed with and without IR laser.