Lifetimes of Plasmas Induced in Liquids and Ocular Media by Single Nd:YAG Laser Pulses of Different Duration

Abstract

The luminescence of plasmas induced by single Nd:YAG laser pulses in distilled water and extracted calf vitreous has been measured with three pulse widths ranging from nanoseconds to tens of picoseconds. The luminescence curves exhibit, for picosecond and subnanosecond pulses, a temporal behaviour characterized by a fast initial transient (of the order of hundreds of picoseconds) which predominates over an exponential component with decay time of the order of the nanosecond. The peak amplitude of the slow component decreases as the laser intensity is increased above threshold. Luminescence decay curves under nanosecond excitation closely follow, at threshold, the temporal shape of the laser pulse. Luminescence quenching is observed at higher intensity. The role of electron-ion recombination and electron attachment to neutral molecules is discussed in relation to the observed luminescence behaviour of the liquids. These observations are useful in the analysis of possible mechanisms of interpulse shielding when trains of mode-locked pulses are used to produce optical breakdown in liquids.