The ion microscope as a tool for imaging the ion distribution produced by linear and non-linear processes at the focus of an XUV beam

We demonstrate a tool for quantitative measurements in the linear and non-linear extreme ultraviolet (XUV) spectral region measuring spatially resolved atomic ionization products at the focus of an XUV beam [1, 2]. The ionizing radiation is a comb of the 11th-15th harmonics of a Ti:Sapphire femtosecond laser beam produced in a Xenon gas jet. The spatial ion distribution at the focus of the harmonics is recorded using an ion microscope detector [2, 3]. Spatially resolved single- and two-photon ionization products of Argon and Helium are observed. From such ion distributions single- and two-photon generalized cross sections have be extracted by a self-calibrating method. This is the first observation of spatially resolved two-XUV-photon ionization at the focus of the XUV radiation which constitutes an important step towards future single-shot temporal characterization of attosecond (asec) pulses [4].