1. Light Diffraction and its Use in the Study of Acoustic Parametric Oscillations
Michael S. McPherson
University of Mississippi
National Center for Physical Acoustics
University, MS 38677

2. Colleagues
Mack Breazeale, Distinguished Professor of Research, UM, University, MS
Alem Teklu, Ph. D., LSU, Asst. Prof., Charleston

3. Block Diagram of Apparatus

5. Diffraction showing existence of subharmonics
Simultaneous Diffraction Patterns and Schlieren Images
(a) without, (b) with Parametric Oscillation

6. Spectrum of Acoustical Parametric Oscillator (l0 = 7.5 cm)

7. Diffraction before and after the onset of of parametric resonance at different frequencies and amplitudes

8. Reflector
Driver l0
The Periodically Varying Cavity

9. Adler’s Data: Threshold Amplitude vs. Frequency

10. Current Data: Threshold Amplitude vs. frequency

17. Conclusions
Results of a new investigation of parametric resonance in an acoustic resonator are presented
Measurements of the threshold drive amplitude frequency dependence show an apparent contradiction with previous results
Resonators with differing lengths can result in the onset of parametric amplification in different regions of instability
These differing regions of instability account for the differences in the observed data trends