PHONON-FOCUSING EFFECT WITH LASER-GENERATED ULTRASONIC SURFACE-WAVES

Surface-phonon focusing is examined with laser generation of pulsed su rface acoustic waves (SAW's). Before presentation of the experimental results, the theory of the effect is summarized including both the ray approach and the stationary-phase analysis. To create a point source of SAW's the focused beam of a Q-switched Nd:YAG (yttrium aluminum gar net) laser is employed. To visualize the SAW amplitude distribution we use dust patterns arising as a result of SAW-induced dust-particle re moval from the surface under investigation. The SAW amplitude measurem ents with the probe beam deflection technique show that the above patt erns reflect adequately the SAW amplitude angular dependence. The stro ng SAW focusing is observed on cubic crystals such as Si, Ge, GaAs, as well as on LiNbO3 crystal. The results obtained are discussed in comp arison with the theory.