Increasing the frequency of surface acoustic waves generated by phase velocity scanning of laser interference fringes

To nondestructively detect surface defects that reduce the strength of cera mics and structural materials of micromachines, we previously developed the phase velocity scanning method. By using scanning interference fringes gen erated by two laser beams whose frequencies are shifted, the method can gen erate a 110 MHz surface acoustic wave (SAW). However, the frequency of the SAW depends on the frequency of the Bragg cell used, thus making the upper- limit frequency about 110 MHz. In this study, we propose multiple use of Br agg cells in series, and successfully generated a 200 MHz SAW. (C) 1999 Ame rican Institute of Physics. [S0034-6748(99)02911-1].