1. Laboratoire Interactions,
Dynamique et Lasers, IRAMIS, CEA-Saclay, 91191 Gif-sur-Yvette, France
2. Department
of Physics, Lund University, P.O. Box 118, SE-22100 Lund, Sweden
3. Laboratorium
für Physikalische Chemie, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland
4. Helmholtz-Institute-Jena, Fröbelstieg 3, 07743 Jena, Germany
5. Laboratoire de
Chimie Physique-Matière et Rayonnement, UMR 7614, UPMC Univ. Paris 06, 11 Rue Pierre et Marie Curie, 75231 Paris Cedex 05, France
6. Department
of Physics, The Ohio State University, Columbus, Ohio 43210, United States