1. R. M. Dickson, D. J. Norris, W. E. Moerner, Department of Chemistry and Biochemistry, Mail Code 0340, University of California, San Diego, 9500 Gilman Drive, La Jolla, CA 92093-0340, USA.
2. Y.-L. Tzeng, Scripps Research Institute, 10666 North Torrey Pines Road, La Jolla, CA 92037, USA.