Manuscript received August 5;
1987;
revised September 10;
1987. This work was supported in pan by the U.S. Air Force Office of Scientific Research under Grant 85-02 13 and by the National Science Foundation Presidential Young Investigator Program under Grant ECS-8552701. The work of J. G. Fujimoto was supported by the Spectra Physics Corporation. the Newport Corporation;
and the Coming Corporation;