HIGH RESOLUTION IMAGING WITH SCANNING LASER ACOUSTIC MICROSCOPY USING DIGITAL IMAGE PROCESSING.

Several factors which contribute to the degradation of SLAM imagery are identified and discussed. These include (1) variable optical intensity due to both laser intensity fluctuations and spatially varying sample or coverslip reflectivity and (2) the mixing of the elastic response of the sample surface and cover slip with the impinging elastic wavefronts which contain the desired image information. A computer-controlled SLAM and several spatial frequency filtering algorithms are described that significantly mitigate these problems. Several images obtained from test samples are presented that illustrate these points. The digitally processed SLAM images are comparable in quality to those that a scanning acoustic microscopy operating at the same acoustic frequency (100 MHz in this study) could produce.