Optical field dependence of breakdown in liquids by Q-switched lasers

Probabilistic behavior of optical breakdown in water is investigated as a function of the laser intensity using Q-switched 1.06 /spl mu/m and 0.532 /spl mu/m lasers with 5-6 ns duration and is compared with the breakdown probability of air in which a avalanche mechanism is believed to govern the breakdown process. These results suggest us a mechanism of optical breakdown is the following. Initial electrons are supplied from liquid itself or impurities in liquids by multiphoton absorption process. These seed electrons absorb laser radiation thorough collision with liquid molecules (microwave breakdown process) and acquires sufficient energy to induce avalanche ionization of liquid molecules.