E. Frumker1,2,3,*, C. T. Hebeisen1, N. Kajumba1,4, J. B. Bertrand1, H. J. Wörner1,5, M. Spanner6, D. M. Villeneuve1, A. Naumov1, and P. B. Corkum1,† 1Joint Attosecond Science Laboratory, University of Ottawa and National Research Council of Canada, 100 Sussex Drive, Ottawa, ON K1A 0R6, Canada 2Max-Planck-Institut für Quantenoptik, Hans-Kopfermann-Strasse 1, D-85748 Garching, Germany 3Department of Physics, Texas A&M University, College Station,Texas 77843, USA 4Department für Physik der Ludwig-Maximilians-Universität, Schellingstrasse 4, D-80799 Munich, Germany 5Laboratorium für physikalische Chemie, ETH Zürich, Wolfgang-Pauli-Strasse 10, 8093 Zürich, Switzerland 6Steacie Institute for Molecular Sciences, National Research Council of Canada, Ottawa, ON K1A 0R6, Canada
Received 12 April 2012; published 12 September 2012
We produce oriented rotational wave packets in CO and measure their characteristics via high harmonic generation. The wave packet is created using an intense, femtosecond laser pulse and its second harmonic. A delayed 800 nm pulse probes the wave packet, generating even-order high harmonics that arise from the broken symmetry induced by the orientation dynamics. The even-order harmonic radiation that we measure appears on a zero background, enabling us to accurately follow the temporal evolution of the wave packet. Our measurements reveal that, for the conditions optimum for harmonic generation, the orientation is produced by preferential ionization which depletes the sample of molecules of one orientation.