Role of a dissolved gas in the optical breakdown of water

It is shown experimentally that the optical breakdown in water produced by nanosecond pulses is initiated by a gas dissolved in it due to the formation of bubston clusters playing the role of heterogeneous seeds of the breakdown. By using the method proposed in the paper, a completely degassed water is obtained, which is optically stable to the seed mechanism of breakdown both away and near the boiling point. The existence of long-lived hydrates of a dissolved gas in water is established and a new effect of water purification from such hydrate traps by 'washing' it with helium is discovered.