1. a Department of Physics and Astronomy , State University of New York , Stony Brook, New York , 11794-3800 , USA
2. b Naval Research Laboratory , Washington , DC , 20375-5345 , USA
3. c Department of Physics , University of Maryland at College Park , College Park, Maryland , 20742-4111 , USA
4. d Department of Applied Science , University of California at Davis , Davis , California , 95916 , USA