Angular distribution and circular dichroism in the two-colour XUV+NIR above-threshold ionization of heliumстатья
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Дата последнего поиска статьи во внешних источниках: 30 марта 2016 г.
Аннотация:The photoelectron angular distribution and the circular dichroism in two-colour XUV+NIR abovethreshold
ionization of helium atoms have been investigated both experimentally and theoretically.
Circularly polarized XUV pulses from the free electron laser FERMI have been spatially and temporally
overlapped with circularly polarized optical pulses in the interaction region with an atomic helium
jet. The emitted electrons were energy and angle analyzed by means of a velocity map imaging
spectrometer. Asymmetry parameters of the angular distribution were determined and compared
to theoretical predictions based on the strong field approximation and perturbation theory,
respectively. For low NIR intensities, the ratio of the partial waves in the two-photon ionization
process and their relative phase could be deduced. For high NIR intensities, the influence of
multi-photon processes is discussed. Circular dichroism was revealed in both cases and is in good
agreement with the results of the strong field approximation.