Strong Focusing of Coherent Terahertz Sound. Final Report, June 1979-November 1981

摘要

The possibility of generating terhertz sound waves at the surface of a gallium arsenide crystal, of spherical convex shape was studied in order to provide strong focusing of very high frequency acoustic energy. The study has included a theoretical investigation of phase and group velocities in GaAs, an attempt to detect phonons via a phonon-electric effect, an observation of strong long-lasting far infrared photoconductivity in epitaxial GaAs layers, and a measurement of an upper limit of phonon mean free paths at 4 exp 0 K. It has been found that the relevant mean free path is too short in chromium doped semi-insulating GaAs to permit the strong focusing originally envisaged.