Spurious acoustic modes in two-dimensional Fourier transform devices

Experiments conducted on two-dimensional (2D) Fourier transform sensors using CdS films on z-cut LiNb03 show evidence for the presence of more than one acoustic velocity in the substrate. Pulsed experiments conducted with two transducers and detailed measurements of transducer frequency response confirm the presence of these additional modes. As a result, the Fourier transform of any image repeats itself in frequency space, the number of repetitions depending on the number of additional acoustic modes. The detrimental effects of these spurious modes can be eliminated entirely by suitable sampling of the image projected on the sensor.