A method is described for 2-D control of spatial coherence by use of multiple, crossing ultrasonic waves. If all the ultrasonic waves differ in frequency from one another, the coherence modification factor results as a product of the individual modification factor formed by each ultrasonic wave itself. Two arrangements are discussed in detail together with experimental results: one with the ultrasonic waves propagating in orthogonal directions, the other with the waves propagating in three symmetric directions. The coherence modification factor obtained from either arrangement varies periodically in space but is almost uniform in the azimuthal direction if the two-point separation concerned is taken in a linear dimension a little larger than half of one ultrasonic wavelength.
© 1983 Optical Society of America
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