Control of the acoustic waves generated by intense laser filamentation in water.

Experiments and simulations are performed to study filamentation and generation of acoustic waves in water by loosely focused multi-millijoules laser pulses. When the laser pulse duration is increased from femtosecond to nanosecond duration, a transition is observed from a filamentary propagation with extended and low energy density deposition to a localized breakdown, related to high energy density deposition. The transition suggests that Kerr self-focusing plays a major role in the beam propagation dynamics. As a result, the shape, the amplitude and the spectrum of the resulting pressure wave present a strong dependence on the laser pulse duration.