Angular distribution and circular dichroism in the two-colour XUV+NIR above-threshold ionization of helium

T. Mazza, M. Ilchen, A. J. Rafipoor, C. Callegari, P. Finetti, O. Plekan, K. C. Prince, R. Richter, A. Demidovich, C. Grazioli, L. Avaldi, P. Bolognesi, M. Coreno, P. O'Keeffe, M. Di Fraia, M. Devetta, Y. Ovcharenko, V. Lyamayev, S. Düsterer, K. UedaJ. T. Costello, E. V. Gryzlova, S. I. Strakhova, A. N. Grum-Grzhimailo, A. V. Bozhevolnov, A. K. Kazansky, N. M. Kabachnik, M. Meyer

Research output: Contribution to journalArticlepeer-review

14 Citations (Scopus)


The photoelectron angular distribution and the circular dichroism in two-colour XUV+NIR above-threshold 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.

Original languageEnglish
Pages (from-to)367-382
Number of pages16
JournalJournal of Modern Optics
Issue number4
Publication statusPublished - 2016 Feb 21


  • Photoionization
  • angular distribution of photoelectrons
  • circular dichroism
  • free electron lasers
  • two-colour experiments

ASJC Scopus subject areas

  • Atomic and Molecular Physics, and Optics


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