Spatially resolved surface acoustic wave studies for image processing

The interaction between a surface acoustic wave (SAW) and photogenerated charge carriers in a piezoelectric semiconductor substrate leads to pronounced changes in the transmission properties of the SAW. Depending on the charge carrier density one observes an attenuation and a change in sound velocity in a SAW delay line comprising a light sensitive semiconductor film. Using specially designed surface acoustic wave transducers, we are able to spatially resolve this interaction. The transducers used for this purpose consist of fan shaped interdigitated metal fingers, which show a broadband frequency transmission. It turns out, that for such transducers the excited SAW propagates on a narrow path, whose position can be controlled by the driving frequency. We axe able to reconstruct a 2D charge distribution by applying a tomographic technique or by nonlinear interaction between a probe and a perpendicular pump SAW crossing each other in the area where charge carriers axe generated.