  We report the application of the time gated ion microscopy technique in
accessing online the position of the source of harmonics generated in atomic
gas media. This is achieved by mapping the spatial extreme-ultraviolet
(XUV)-intensity distribution of the harmonic source onto a spatial ion
distribution, produced in a separate focal volume of the generated XUV beam
through single photon ionization of atoms. It is found that the position of the
harmonic source depends on the relative position of the harmonic generation gas
medium and the focus of the driving infrared (IR) beam. In particular, by
translating the gas medium with respect to the IR beam focus different virtual
source positions are obtained online. Access to such online source positioning
allows better control and provides increased possibilities in experiments where
selection of electron trajectory is important. The present study gives also
access to quantitative information which is connected to the divergence, the
coherence properties and the photon flux of the harmonics. Finally, it
constitutes a precise direct method for providing complementary experimental
info to different attosecond metrology techniques.
