Diffractive acoustic elements for laser ultrasonics

Laser ultrasonics is an effective means of generating surface acoustic wave s (SAWs). We have shown in previous publications how computer-generated hol ograms (CGHs) can be used to project optical distributions onto the sample surface. These can be used to control both the frequency content and the sp atial distribution of the resulting ultrasound field. In this paper the con cept is extended further to produce distributions which themselves act as d iffractive acoustic elements (DAEs) for SAWs. It is demonstrated how freque ncy suppression, multiple foci, and frequency selective focusing of Rayleig h waves may be achieved with these elements. Agreement between the distribu tions predicted from the designs and those actually measured is excellent. (C) 2000 Acoustical Society of America. [S0001-4965(00)05006-2].