Nonlinear propagation of laser-generated sound pulses in a water and granular medium

Nonlinear propagation of finite-amplitude acoustic pulse in water and throu gh a sample of water-saturated granular medium is considered. To generate h igh-intensity acoustic pulses laser generation of sound was used. The regio n of fluid perturbed by the laser acts as a volume-distributed source. In a fluid with weak light attenuation, a cylindrical source could be formed by a narrow laser beam. The nonlinear distortion of the cylindrical finite-am plitude wave in water is investigated. The measured rate of distortion corr esponds to that calculated:in the approximation of nonlinear acoustics. In a strongly light-absorbing medium, a wide (compared to the typical sound wa velength) laser beam produces a circular planar source. Such a source produ ces acoustical pulses of amplitude up to 3 MPa and duration about I mu s in different fluids. This source was used to investigate the propagation of h igh-intensity wide frequency band sound signals:in a sample of water-satura ted cobalt-manganese crust (CMC). Specific acoustical features of:the crust such as nonlinear sound pulse distortion and the frequency dependance of a ttenuation, varying with the amplitude, are considered. Theoretical interpr etation of the results is given. (C) 1999 Acoustical Society of America. [S 0001-4966(99)04512-9].