Observation of nonlinear evolution of acoustic pulses in the absence of diffraction

The results of experiments are discussed in which a nonlinear evolution of acoustic pulses was observed under specially chosen conditions, where the effect of diffraction was practically ruled out. Acoustic pulses were generated by an optoacoustic method, which enables one to obtain short powerful pulses of predictable shape. The pulses were picked up by a hydrophone based on a polyvinylidene fluoride film. At high peak pressures the evolution of an almost triangular profile with a clearly pronounced discontinuous front was observed. The pulse amplitude decreased in inverse proportion to the root of the distance to the radiator. The experimental results are in good agreement with the classical theory of such waves.