Acoustooptic formation of a periodic coherence function and its utility in double-slit imaging

The use of acoustically phase-modulated coherent light is described for producing a periodic optical coherence function. A progressive acoustic wave, working as an optical phase object, converts a coherent optical wave into a periodically incoherent optical wave in the far field, which forms an array of secondary periodic incoherent sources. This array further produces a periodically partially coherent wave in its far field. These aspects are fully explained in terms of the propagation law of optical mutual intensity in the double-diffraction imaging system. A purely cosinuosoidal type of mutual intensity, consisting of three fundamental spatial-frequency components of the acoustically phase-modulated optical field, is created and ensured experimentally. Its variational depth is almost controllable with an ac electric field across the acoustic transducer. Image resolution of a double-slit object under such a periodically partially coherent illumination is discussed. The image obtained is resolved and enhanced at the double-slit separation of half of the acoustic waveleneth.