Light Diffraction by Ultrasonic Waves—Fresnel Region

The time dependence of the intensity of the light in the Fresnel region diffracted by a progressive wave is measured directly. The measurements are compared to the theory of a periodic moving grating. Suggestions are made for measuring the harmonic content of the wave and the fundamental wavelength of the grating. Examples are given of the available periodic intensity fluctuations, and a method for determining relative pressures is suggested. This paper gives the details of work that was reported at the Fourth International Congress on Acoustics (K. L. Zankel and H. M. Colbert, Fourth International Congress on Acoustics, Copenhagen, 21–28 August 1962).