Diffraction of Light by Finite Amplitude Ultrasonic Waves

In the late 1950s the Ultrasonic Group at Michigan State University introduced light diffraction to study distortion of ultrasonic waves in liquids under the direction of Prof. Egon Hiedemann. In this paper some results of these studies will be presented with detailed description of the author's measurements of B/A. The rate at which the harmonics are developed (the wave distortion is an indication of the harmonics present) during the propagation of the initially sinusoidal ultrasonic wave depends on the nonlinearity of the medium. The light which is diffracted by the distorted wave results in asymmetric pattern contrary to the Raman-Nath theoretical prediction. From the light intensity measurements due to the generated second harmonics - filtered out by a metal plate - the nonlinearity parameter B/A was determined. Developments in studying finite amplitude standing ultrasonic waves in a liquid filled cavity will be also discussed. Using light diffraction measurements it was observed that above a threshold amplitude, fractional harmonics of the driver transducer are also generated in addition to the generated harmonics. It was recently observed that above a second threshold value of the driver amplitude the system undergoes chaotic behavior. Further increase of the driver amplitude returns the system from chaos to stable oscillation