1. Research Group on Laser Physics of the Hungarian Academy of Sciences, H-6701 Pf. 406 Szeged, Hungary (Z. Bozóki); Department of Optics and Quantum Electronics, University of Szeged, H-6701 Pf. 406 Szeged, Hungary (A.M., G.S., Z. Bor); and Rice Quantum Institute, Rice University, Houston, Texas 77005 (M.E., W.C., F.K.T.)