Determination of the nonlinear ultrasonic parameter using a Michelson interferometer

We describe an accurate optical technique for determining the nonlinear ultrasonic parameter . Our technique uses a path-stabilized Michelson laser interferometer, in contrast to more conventional methods which use piezoelectric or capacitive detectors. Features include high spatial resolution (typically ), flat bandpass response over a wide range (> 30 MHz) and simple self-calibration. We demonstrate the technique using a fused silica disc 19.15 mm thick and a fundamental frequency of 10 MHz. For comparison, was also obtained for the same specimen using capacitive and piezoelectric detectors. Errors and correction factors for all three methods are discussed; in particular, we note the importance of including ultrasonic diffraction effects. When such corrections are applied, we obtain the following These values are in reasonable agreement with each other as well as with published values of .