Berlin 2014 – scientific programme
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A: Fachverband Atomphysik
A 35: Poster: Interaction with VUV and X-ray light
A 35.14: Poster
Wednesday, March 19, 2014, 16:30–18:30, Spree-Palais
Multi-photon ionization processes in rare gases — •Sadegh Bakhtiarzadeh1,2, Tommaso Mazza1, Markus Ilchen1, and Michael Meyer1 — 1European XFEL GmbH, Hamburg, Germany — 2Department of Physics, University of Hamburg, Hamburg, Germany
Interaction of photons with matter has been subject to studies for a long time. Recently, it has entered a new area with the availability of intense VUV or X-ray Free Electron Lasers (FEL), where the short wavelength radiation can couple efficiently to inner electronic shells of the atoms. In this regards, we have performed a series of experiments on rare gases, especially Ar and Xe, using three different photon energies (105, 123 and 140 eV) from FLASH, Hamburg, Germany. Using a multilayer mirror the FEL beam was focused to a spot size of 5 µm diameter, i.e. intensities in the order of 1014 W/cm2 could be reached. Under such high intensities, different ionization processes can happen, of which the most important are the two-photon sequential as well as the two-photon direct ionization. The relative importance of the individual channels has been investigated by energy-resolved electron spectroscopy. As additional proof for the non-linearity of the process the intensity dependence of the electron emission was monitored. For the expected quadratic dependence of the two-photon processes, an exponent smaller than 2 was generally observed. This can be explained by the extended acceptance angle in the experiment requiring proper volume integration, i.e. a careful consideration of regions with different intensities.