1. Material Measurement Laboratory, National Institute of Standards and Technology, Gaithersburg, Maryland 20899, USA
2. School of Electrical and Computer Engineering and Birck Nanotechnology Center, Purdue University, West Lafayette, Indiana 47907, USA
3. Nano-Meta Technologies, Inc., 1281 Win Hentschel Boulevard, West Lafayette, Indiana 47906, USA
4. Center for Ultrafast Optical Science, University of Michigan, Ann Arbor, Michigan 48109, USA