1. Biophysics Graduate Group, University of California, Davis, California 95616, NSF Center for Biophotonics Science and Technology, UC Davis, Sacramento, California 95817, Department of Pediatrics, UC Davis Medical Center, Department of Pathology and Laboratory Medicine, UC Davis Medical Center, Sacramento, California 95820, Department of Applied Science, University of California, Davis, California 95616, and Physics Division, Lawrence Livermore National Laboratory, Livermore, California 94550