Experimental Investigation of Optical Breakdown Thresholds in Ocular Media under Single Pulse Irradiation with Different Pulse Durations

Abstract

Curves of probability of occurrence of optical breakdown have been plotted in respect to measurements carried out in liquids used as models for ocular media. These studies also included exposures in calf vitreous.
\nThe Nd:YAG lasers used were able to deliver single pulses at the fundamental wavelength with three different
\npulse durations, i.e., 7 ns.220 and 30 ps respectively, in three different focusing conditions. The results show
\nthat breakdown threshold intensities increase substantially with decreasing the pulse duration, an observation
\nsimilar to that found in solids. In addition, breakdown curves obtained with picosecond pulses are steeper
\nthan those obtained with nanosecond pulses, thus showing that with shorter pulses the process of onset of
\nbreakdown is more deterministic. Impurities are shown to play a decreasing role in the initiation of the process of optical breakdown as the pulse duration is decreased.
\nFinally it has been found that, with tight focusing, the breakdown threshold intensity increases much more
\nwith picosecond pulses than with nanosecond pulses.
\nThe importance of these observations both for the characterization of different laser disruptors and for
\nthe clinical use of the Nd:YAG laser in ophthalmic microsurgery will be discussed.