The role of self-focusing in laser-induced breakdown of water caused by nano- and picosecond pulses

An experimental investigation of laser-induced breakdown of water and subthreshold phenomena using pulsed laser radiation in the nanosecond to picosecond region has been performed. It has been shown that self-focusing and suspended particles have a strong influence on laser-induced breakdown of water. A significant decrease in transmittance for an input irradiance 1 to 2 orders of magnitude less than the laser-induced breakdown threshold of water as observed, as well as a strong spot size dependence of this threshold. Besides the investigated processes result in a breakdown threshold of water for small spot sizes (∼2-4μm) that is nearly 10 times larger than that of glass due to a sharp increase in scattering from inhomogeneities formed as a result of self- focusing. For large spot sizes (∼20μm) the breakdown threshold of water is considerably less than for the same glasses (∼10-100 times) due to breakdown initiated by suspended particles. ©2004 Copyright SPIE - The International Society for Optical Engineering