[1] Univ Jena, Inst Opt & Quantenelekt, D-07743 Jena, Germany
[2] Helmholtz Inst Jena, D-07743 Jena, Germany
[3] Max Planck Inst Quantum Opt, D-85748 Garching, Germany
[4] Kansas State Univ, Dept Phys, JR Macdonald Lab, Manhattan, KS 66506 USA
[5] Tech Univ Munich, D-85748 Garching, Germany
[6] Texas A&M Univ, Dept Phys, College Stn, TX 77843 USA