1. Department of Chemistry, Duke University, Durham, North Carolina 27708, United States
2. Army Aviation & Missile RD&E Center, Redstone Arsenal, Alabama 35898, United States
3. Optics Group, Department of Applied Physics, University of Cantabria, Avda de Los Castros, s/n 39005 Santander, Spain
4. Department of Physics, Duke University, Durham, North Carolina 27708, United States