[1] CALTECH, Jet Prop Lab, Pasadena, CA 91125 USA
[2] MIT, Dept Elect Engn & Comp Sci, Cambridge, MA 02139 USA
[3] CALTECH, Dept Appl Phys, Pasadena, CA 91125 USA
[4] Natl Inst Stand & Technol, Boulder, CO USA
[5] Fermilab Natl Accelerator Lab, POB 500, Batavia, IL 60510 USA
[6] CALTECH, Div Phys Math & Astron, Pasadena, CA 91125 USA
[7] Calif State Univ Los Angeles, Dept Elect & Comp Engn, Los Angeles, CA 90032 USA
[8] Univ Lancaster, Dept Phys, Lancaster, England