  Acoustic signals generated by filamentation of ultrashort TW laser pulses in
water are characterized experimentally. Measurements reveal a strong influence
of input pulse duration on the shape and intensity of the acoustic wave.
Numerical simulations of the laser pulse nonlinear propagation and the
subsequent water hydrodynamics and acoustic wave generation show that the
strong acoustic emission is related to the mechanism of superfilamention in
water. The elongated shape of the plasma volume where energy is deposited
drives the far-field profile of the acoustic signal, which takes the form of a
radially directed pressure wave with a single oscillation and a very broad
spectrum.
