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

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

Block Diagram of Apparatus

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

Spectrum of Acoustical Parametric Oscillator (l0 = 7.5 cm)

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

Reflector Driver l0 The Periodically Varying Cavity

Adler’s Data: Threshold Amplitude vs. Frequency

Current Data: Threshold Amplitude vs. frequency

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