Fraunhofer Diffraction of Light and of Ultrasonic Waves by Gratings having Multiple Periodicities.
TENNESSEE UNIV KNOXVILLE ULTRASONICS LAB
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The theory of Fraunhofer diffraction of light by coherently illuminated amplitude transmission gratings having an arbitrary number of periodicities has been developed by Fourier transform techniques. This mathematical description has been specialized for the case of a grating having a double periodicity. The resulting expression has been tested experimentally. In addition, the case of the singly-periodic grating was also considered. In each case agreement between theory and experiment was found to be reasonable in the lower diffraction orders. In the higher diffraction orders, the agreement was not as good. An ultrasonic schlieren apparatus made it possible to model the optical experiment with an analogous acoustical one. Photographs of the diffraction of ultrasonic waves by gratings having single and double periodicities were made. Qualitative comparison between the optical and acoustical configurations is made.