Angular distribution and circular dichroism in the two-colour XUV+NIR above-threshold ionization of helium. Issue 4 (21st February 2016)

• Record Type: Journal Article
• Authors: Mazza, T.; Ilchen, M.; Rafipoor, A.J.; Callegari, C.; Finetti, P.; Plekan, O.; Prince, K.C.; Richter, R.; Demidovich, A.; Grazioli, C.; Avaldi, L.; Bolognesi, P.; Coreno, M.; O'Keeffe, P.; Di Fraia, M.; Devetta, M.; Ovcharenko, Y.; Lyamayev, V.; Düsterer, S.; Ueda, K.; Costello, J.T.; Gryzlova, E.V.; Strakhova, S.I.; Grum-Grzhimailo, A.N.; Bozhevolnov, A.V.; Kazansky, A.K.; Kabachnik, N.M.; Meyer, M.
• Is Part Of: Journal of modern optics. Volume 63:Issue 4(2016)
• Page Start: 367
• Page End: 382
• Publication Date: 2016-02-21
• Subjects: Photoionization -- free electron lasers -- two-colour experiments -- angular distribution of photoelectrons -- circular dichroism; Optics -- Periodicals; 535
• DOI: 10.1080/09500340.2015.1119897
• Languages: English
• ISSNs: 0950-0340

Abstract

Abstract : 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.