1. Institut für Experimentalphysik, Technische Universität Graz, Petersgasse 16, 8010 Graz, Austria
2. Department of Chemistry and Pharmaceutical Sciences, Faculty of Sciences, Vrije Universiteit Amsterdam, De Boelelaan 1083, NL-1081 HV Amsterdam, The Netherlands
3. Dirac Solutions, 10527 NW Lost Park Drive, Portland, OR 97229, USA
4. Université de Lille, CNRS, UMR 8523 - PhLAM - Physique des Lasers, Atomes et Molécules, F-59000 Lille, France