Material dependence of laser-induced breakdown of colloidal particles in water

Abstract

Laser-induced breakdown of colloidal suspensions, such as polystyrene, ZrO2, and Sio2 particles in diameters of 100-400 nm in water is investigated by nanosecond flash-pumped Nd:YAG laser pulses operating at a wavelength λ = 532 nm. The breakdown threshold intensity is examined in terms of breakdown probability as a function of laser pulse energy. The threshold intensity for SiOa particles (1.27×1011 W/cm 2 ) with a size of 100 nm is higher than those for polystyrene and ZrO2 particles with the same size, namely 5.7×1010 and 5.5×1010 W/cm2, respectively. Results indicate that the absorption of five photons is required to induce ionization of SiOi particles, whereas the other particles necessitate four-photon absorption. These breakdown thresholds are compared with those measured by nanosecond pulses from a diode-pumped Nd:YAG laser having a different focusing geometry.