Diffraction of Light by Ultrasonic Waves Progressing with Finite but Moderate Amplitudes in Liquids

Abstract

The study of the asymmetry of the light diffracted by ultrasonic waves progressing with moderate amplitudes in liquids is used to detect and measure the finite amplitude distortion in water and carbon tetrachloride. A theory is developed which relates the distortion present to available isothermal compressibility measurements. This development includes the presence of absorption.Measurements of the second harmonic were made in water at 2 Mc and 4 Mc, at distances up to 50 cm, and at peak ultrasonic pressures between zero and 1.5 atmos. More detailed measurements were made in carbon tetrachloride at frequencies of 2 and 3 Mc, at distances up to 21 cm, and at pressures up to 0.7 atmos. For both liquids, good agreement is obtained between the experimentally measured values and the theoretically predicted results.Small amounts of distortion were easily measured. The second harmonic could be measured when the intensity of the harmonic was less than 0.04% of the intensity of the fundamental. Distortion could be measured when the fundamental was much less than 0.2 atmos. I. INTRODUCTIONINCE it was discovered that ultrasonic waves could produce diffraction of light, several authors have offered theoretical explanations of the details of this diffraction. Some of these theories •-a are rigorous but very complex and difficult to apply to practical situations. In many cases it is preferable to use an approximate theory which is much simpler to handle and which can be used in an easily obtainable experimental region. This theory, which was developed by Raman and Nath, 4-6 gives satisfactory results in the region of moderately low amplitudes and frequencies.All of the theories predict that there is symmetry about the zero order of diffraction when this diffraction is produced by light incident at right angles to a plane, sinusoidal, ultrasonic wave. In the usual visual observations, one does not hotice any asymmetry. However Sanders, 7 using a photomultiplier, found that an asymmetry between the negative and positive orders appeared to be present. Sette 8 visually observed slight asymmetry at large distances from the sound source. Rao 9 also observed asymmetry and tried to explain it by the generation of second harmonics in the ultrasonic source. Miller •ø very carefully studied this problem and * Submitted by K. L. Zankel in partial fulfillment of the requirements for a Ph.D. degree at Michigan State University. $ This research was sponsored by the Office of Ordnance Research, U.S. Army. • R. Extermann and G. Wannier, Helv. Phys. Acta. 9, 520-532 (1936). . •0 R. B. Miller, thesis, "A study of the intensity distribution of the light diffracted by ultrasonic waves," Michigan State University, East Lansing (1956). 44found that the asymmetry could not be eliminated by adjustments in the equipment. Breazeale and Hiedemann n showed that a similar asymmetry observed with refraction could be explained by finite amplitude distortion. Mikhailov and Shutilov x2 were able to show that for extremely high intensities (which at times appro...

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