1. Center for Bio/Molecular Science and Engineering Code 6900, U.S. Naval Research Laboratory, Washington, DC 20375, Division of Optical Sciences Code 5611, U.S. Naval Research Laboratory, Washington, DC 20375, Laboratory for the Structure of Matter Code 6030, U.S. Naval Research Laboratory, Washington, DC 20375, Electronic Science and Technology Code 6812, U.S. Naval Research Laboratory, Washington, DC 20375, and Department of Biomedical Engineering, Georgia Institute of Technology, Atlanta, Georgia 30332