1. Department of Physics and JILA, University of Colorado and NIST, Boulder, Colorado
80309, United States
2. Department
of Chemistry and
Biochemistry, University of Colorado, Boulder,
Colorado 80309, United States
3. Department of Chemistry and Biochemistry
and CIRES, University of Colorado, Boulder,
Colorado 80309, United States
4. Quantum Electronics and Photonics
Division, NIST, Boulder, Colorado 80305,
United States