HIGH RESOLUTION BACKPROJECTION IMAGING WITH A SCANNING LASER ACOUSTIC MICROSCOPE.

A back-projection imaging capability has been implemented on a scanning laser acoustic microscope, which permits the reconstruction of clear well-defined images of acoustic features which are far below (by tens of acoustic wavelengths) the laser-scanned surface. Several types of test features have been imaged, including electron microscope locator grids affixed to the bottom side of glass slides and etched features (approximately 5- mu m deep) on a thick (1 cm) glass block. 100-MHz insonification was used and features with lateral dimensions of roughly 50 mu m could be distinguished. Using the same database, two separate images of a feature could be brought into focus, one corresponding to compressional waves and the other to shear waves.