1. Department of Electrical Engineering and Computer Science and Research Laboratory of Electronics,, Massachusetts Institute of Technology, Cambridge, MA 02139.
2. Lincoln Laboratory, Massachusetts Institute of Technology, Lexington, MA 02139.
3. Department of Ophthalmology, Harvard Medical School and the Laser Research Laboratory, Massachusetts Eye and Ear Infirmary, Boston, MA 02114.
4. Wellman Laboratories, Massachusetts General Hospital, Boston, MA 02114.