Pulsed laser-induced material ablation and its clinical applications
Abstract
Removing portions of a material, using a laser is referred to as laserinduced
material ablation. The general goal of laser ablation is the efficient
removal of material with minimum damage to the surrounding region. The
appropriate selection of laser parameters, which determine the ablation
mechanism, is essential to achieving a successful outcome. The research
described in this dissertation was designed to evaluate the ablation mechanisms
associated with pulsed lasers operating with different pulse durations and their
medical applications.
The role of a transparent liquid layer during a laser ablation process was
studied. In comparison with a dry ablation process, the liquid-assisted ablation
process resulted in augmented ablation efficiency and reduced ablation threshold.
The results indicate that increased photon energy conversion to mechanical
energy is responsible for the enhanced material ablation.
Transparent targets were exposed to the one picosecond mid-IR pulse in
order to investigate the origin of laser-induced surface damage. The results
indicate that the surface damage was initiated by the laser-induced plasma created
through the optical breakdown process.
The retropulsive momentum of calculus during the Ho:YAG laser
lithotripsy was measured using a high speed camera. The correlation between
laser-induced crater shape, the trajectory of debris, and the retropulsive
momentum is discussed.
Due to the strong interaction between the laser pulse and calculus, the
endoscopic delivery fiber may be subjected to damage resulting in diminished
fragmentation efficiency. Deterioration of the delivery fiber during lithotripsy
was quantified in terms of transmission loss and change in exit beam profile.
To test the feasibility of Er:YAG laser lithotripsy, the fragmentation
efficiency of Ho:YAG and Er:YAG lasers was compared. The results suggest
that although the Er:YAG laser produced more precise drilling it did not create
more fragmentation of calculus than the Ho:YAG laser for multiple pulse
processes.
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