1. School of Chemistry and School of Biological Sciences, University of East Anglia, Norwich Research Park, Norwich NR4 7TJ, United Kingdom
2. Department of Physics and Astronomy and Thomas-Young Centre, University College London, London WC1E 6BT, United Kingdom
3. Central Laser Facility, Research Complex at Harwell, Harwell Campus, Didcot, Oxon OX11 0QX, United Kingdom
4. Institute for Advanced Study, Technische Universität München, Lichtenbergstrasse 2 a, D-85748 Garching, Germany