1. Laser Dynamics Laboratory, School of Chemistry and Biochemistry, Georgia Institute of Technology, 770 State Street, Atlanta, Georgia 30332-0400
2. Laboratoire des Matériaux Mésoscopiques et Nanométriques, UMR CNRS 7070, Université Pierre et Marie Curie, BP 52, 4 place Jussieu, 75252 Paris Cedex 05, France, and School of Chemistry and Biochemistry, Georgia Institute of Technology, 770 State Street, Atlanta, Georgia 30332-0400