Plasma dynamics of water breakdown at a water surface induced by femtosecond laser pulses

Femtosecond laser pulse induced ultrafast plasma dynamics studies of water breakdown in the range up to $250\mathrm{ps}$ are reported. We combine transient imaging techniques together with spectrally resolved reflection spectroscopy to monitor the early breakdown dynamics at the water surface with a laser intensity being 1.5 above threshold. We observe a $20\mathrm{ps}$ delay before the plasma expands with an initial velocity of $5900\mathrm{m}∕\mathrm{s}$ . The transient electron density after formation of the plasma is $1.2\times {10}^{21}∕{\mathrm{cm}}^3$ . A recombination on a picosecond time scale with a rate of $(1.6\times {10}^{-9}\pm 0.3\times {10}^{-9}){\mathrm{cm}}^3∕\mathrm{s}$ is found.