Visualization of surface acoustic waves by means of synchronous amplitude-modulated illumination

A simple technique for visualizing two-dimensional traveling surface acoustic wave (SAW) phenomena in real time was developed. The technique requires illumination of a SAW carrying substrate with a collimated, sinusoidally amplitude-modulated laser beam. Though at first the technique may appear to be stroboscopic in nature, it in fact has its foundations in spatiotemporal correlation theory. It is shown that if the modulation frequency of the illumination beam is equal to, or an integer fraction of, the SAW frequency (i.e., if they are temporally correlated) then, after simple spatial filtering, high-visibility stationary fringes can be produced. In fact, it is shown that a maximum fringe visibility of nearly 60% can be achieved. It is believed that this is the highest visibility yet reported for similar SAW visualization techniques.