Forward dynamics of water-plasmas produced by femtosecond laser pulses

The evolution of the forward density front of water-plasmas generated by ultrashort laser pulses on an air–water interface is investigated with optical diagnostics. The density front is found to move with supersonic speed at the beginning, as predicted by a hydrodynamics simulation. This plasma-expansion process is followed by a fluid mechanical process. The expansion rate gradually reduces to the acoustic speed in water.