Abstract: A proton exchange polarizer with a spatial filter positioned to reduce cross coupling of unguided radiation. A photoconductor substrate is fabricated from LiNbO.sub.3 or LiTaO.sub.3. The substrate has a spatial filter located at a primary reflection point on a bottom of the substrate so as to block unguided TM mode light from reaching the output of the substrate. The spatial filter is fabricated by physical or chemical methods such as saw cutting, diamond machining, etching, micro-machining, laser-machining and/or damaging the surface of the substrate. The unguided TM mode light is attenuated by blockage or interruption of the transmissive region.

Abstract: Electronically changing the effective element spacing of an array of acoustic transducer elements between the transmit and receive modes of operation of an ultrasound apparatus results in reducing the deleterious effects of grating lobes present in the pattern of the array because of element spacings in excess of one half of a wavelength. A linear or quadratic time delay distribution, or both simultaneously, is applied to the array for scanning and/or focusing by setting individually the time delay of the energy associated with each element of the array during one mode of operation, e.g. transmit. The array is organized into groups of elements, e.g. pairs, and the time delay distribution is applied by setting the time delay of the energy associated with each group of the array during the remaining mode of operation, e.g. receive.