Experimental comparison of ultrasonic techniques to determine the nonlinearity parameter beta

We describe experiments to evaluate the use of an infrared Michelson interferometer as a quantitative probe of nonlinear ultrasonic propagation. This technique exhibits several distinct advantages over previous methods using capacitive or piezoelectric detectors, including high spatial resolution (typically 10 mu m), flat broadband response (up to 300 MHz), and simple self-calibration. The method is evaluated by determining the nonlinearity parameter IPI in a fused silica specimen, and comparing the results to those obtained for the same specimen using a capacitive receiver and a piezoelectric transducer. When ultrasonic diffraction effects are included, values for \beta\ are in good agreement with the literature values of \beta\ = 11-14. These results indicate that optical methods can be used for practical and accurate detection of nonlinear ultrasound.