1. Department of Physics and Astronomy, University of Georgia, Athens, Georgia 30602-2451, United States
2. Department of Mechanical Engineering, Vanderbilt University, Nashville, Tennessee 37212, United States
3. U.S. Naval Research Laboratory, Washington, D.C. 20375, United States
4. J. A. Woollam Co., Inc., Lincoln, Nebraska 68508, United States
5. Institute of Experimental Physics, Freie Universität Berlin, Arnimallee 14, Berlin, 14195 Germany