Acoustic-radiation stress in solids. II. Experiment

The first direct experimental evidence for the radiation-stress-induced static strain or displacement associated with the propagation of acoustic waves in solids is reported. Ultrasonic tonebursts launched into samples of single-crystal silicon along the [110] direction and vitreous silica (Suprasil W1) are seen to generate static displacement pulses having the shape of a right-angled triangle. This shape is in agreement with acoustic-radiation-stress theory which also predicts that the slope of the static displacement pulse depends directly on the magnitude and sign of the acoustic nonlinearity parameter of the solid. For silicon the nonlinearity parameter is positive and is seen to give rise to a dilative pulse, while for vitreous silica the nonlinearity parameter is negative and produces a contractive pulse as predicted. Calculations of the acoustic nonlinearity parameters from absolute measurements of the slope of the static displacement pulse and the amplitude of the ultrasonic toneburst yield the values 5.4 for silicon along the [110] direction and --- 12.7 for Suprasil W1. These values are in good agreement with those determined independently from ultrasonic harmonic-generation methods.