Oscillations, Waves, and Interactions - GWDG

Oscillations, Waves and Interactions, pp. 217–258
edited by T. Kurz, U. Parlitz, and U. Kaatze
Universitätsverlag Göttingen (2007) ISBN 978–3–938616–96–3
urn:nbn:de:gbv:7-verlag-1-09-7
Phase transitions, material ejection, and
plume dynamics in pulsed laser ablation
of soft biological tissues
Alfred Vogel 1 , Ingo Apitz 1 , and Vasan Venugopalan 2
1 Institut für Biomedizinische Optik, Universität Lübeck
Peter-Monnik-Weg 4, D-23562 Lübeck, Germany
2 Dept. of Chemical Engineering and Materials Science and
Laser Microbeam and Medical Program, Beckman Laser Institute
University of California, Irvine, California 92697, USA
1 Introduction
After the invention of the pulsed ruby laser by Maiman in 1960 it was anticipated that
lasers would enable the cutting and removal of biological tissue with unprecedented
precision and selectivity [1]. However, even though pulsed lasers were used within a
few years for intraocular tissue coagulation, a clinically viable application of pulsed
laser ablation was not reported until the early 1970’s. It would take until the 1980’s
for lasers to be routinely used for ophthalmic dissection and ablation procedures [2,3].
In other medical sub-specialties routine laser use did not begin until the mid 1980’s.
The delay between the invention of the laser and its successful clinical application
was largely due to a lack of understanding of the fundamental mechanisms that
govern laser–tissue interactions. Now, as we approach the 50th anniversary of the
invention of the laser, the understanding of laser–tissue interactions has matured
and procedures that employ pulsed laser radiation are not only present in nearly
every medical sub-specialty but also in various biological fields.
In the 1990’s, two books on laser–tissue interactions became available and serve
as a valuable resource for the field [4,5]. However, a comprehensive review of the
fundamental mechanisms involved in pulsed laser ablation of tissue appeared only
very recently when Vogel and Venugopalan [6] presented a conceptual framework
providing mechanistic links between various ablation applications and the underlying
thermodynamic and phase change processes. The present article summarizes key
elements of this analysis, with focus on the kinetics of rapid phase transitions in
aqueous media and their modifications by the presence of a tissue matrix. The results
obtained are then used to analyse the mechanisms of material ejection in pulsed
laser tissue ablation and their consequences for ablation efficiency, precision, and
collateral damage. Description of the ablation plume dynamics will be an essential
part of this analysis because the composition of the plume reflects the kinetics of