@article{b1690dd2918e40a1ac58baf1bac6c8e5,
title = "Angular distribution and circular dichroism in the two-colour XUV+NIR above-threshold ionization of helium",
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.",
keywords = "Photoionization, angular distribution of photoelectrons, circular dichroism, free electron lasers, two-colour experiments",
author = "T. Mazza and M. Ilchen and Rafipoor, {A. J.} and C. Callegari and P. Finetti and O. Plekan and Prince, {K. C.} and R. Richter and A. Demidovich and C. Grazioli and L. Avaldi and P. Bolognesi and M. Coreno and P. O'Keeffe and {Di Fraia}, M. and M. Devetta and Y. Ovcharenko and V. Lyamayev and S. D{\"u}sterer and K. Ueda and Costello, {J. T.} and Gryzlova, {E. V.} and Strakhova, {S. I.} and Grum-Grzhimailo, {A. N.} and Bozhevolnov, {A. V.} and Kazansky, {A. K.} and Kabachnik, {N. M.} and M. Meyer",
note = "Funding Information: The authors thank the members of the FERMI Team at Elettra- Sincrotrone Trieste who contributed to this project, including the accelerator operations group, the information technology group, and all engineering support teams. ANG acknowledges hospitality of the European XFEL. The LDM@FERMI beamline acknowledges support by the Regione Autonoma Friuli Venezia Giulia Project ANGEL, PORFESR 2007-2013-Regional Competitiveness and Employment Objective-Activity (1.1.a)2, and by the Italian?Slovenian Crossborder Cooperation Programme (CITIUS project, 2013/201009 0600115298). TM, MI, AJR and MM acknowledge support by the Deutsche Forschungsgemeinschaft (DFG) under [grant number SFB 925/A1]. T.M. and M.M. acknowledge financial support by Elettra within the CALIPSO Transnational Access Program. The participation of J.T.C. is supported under SFI [grant number 12/IA/1742]. NMK acknowledges hospitality and financial support by European XFEL (Hamburg) and by DIPC (Donostia/San Sebastian). He also acknowledges financial support from the programme ?Physics with Accelerators and Reactors in West Europe? of the Russian Ministry of Education and Science. AVB acknowledges the support of St. Petersburg State University [grant number 11.38.654.2013].",
year = "2016",
month = feb,
day = "21",
doi = "10.1080/09500340.2015.1119897",
language = "English",
volume = "63",
pages = "367--382",
journal = "Optica Acta",
issn = "0950-0340",
publisher = "Taylor and Francis Ltd.",
number = "4",
}