Experimental Investigation of Threshold Fluence for Sub-lOOfs Laser Pulse Interaction with Hard and Soft Tissue

Threshold measurements for laser-induced breakdown of different organic tissue (cornea, brain, enamel) and inorganic matter (fused silica) have been extended to the sub-lOOfs time regime. A Ti:Sapphire laser system delivers 450 microjoules at repetition rates up to 1kHz. Single shot experiments are performed with pulse durations from 35fs to 240fs. To ensure a consistent determination of the threshold fluence, damage is detected by the alteration in amplitude of scattered light and/or by the occurrence of a plasma spark. In our single shot experiment with human enamel, no significant threshold dependence on pulse duration was observed. For soft tissue (cornea, brain), however, a slight decrease of threshold fluence is found when shortening the pulse duration. Fused silica is chosen as an additional target to compare the obtained data with those of recent experiments.