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Proceedings Paper

Laser-induced microbubble formation at a fiber tip in absorbing media: experiments and theory
Author(s): Guenther Paltauf; Martin Frenz; Heinz Schmidt-Kloiber
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Paper Abstract

Short laser pulses transmitted through optical fibers are an important tool for minimally invasive surgery. In the regime of temperature and stress confinement these pulses are capable of producing combined mechanical and thermal effects in absorbing media, which are initiated by the formation of micro cavities. Pulses with a duration of 6 ns created by an optical parametrical oscillator (OPO) were guided via a quartz fiber into an aqueous dye solution. The absorption coefficient of the solution could be varied between 24 cm-1 and 900 cm-1 by tuning the wavelength of the OPO. The micro bubble dynamics were observed with time-resolved imaging. Stress transients were measured with piezoelectric detectors. At high absorption the formation of micro bubbles can be seen clearly outside the optically heated zone in front of the fiber tip. At low absorption bubbles are formed in the optically heated zone at temperatures below the boiling point. These observations together with the occurrence of bipolar stress signals support the assumption that thermoelastic stress waves with negative components arising from the limited geometric extension of the stress source are responsible for the generation of the bubbles. Far from the fiber tip this edge effect leads to diffraction of the wave. The hypothesis is further verified by theoretical calculations. In non-contact applications of infrared laser pulses where the radiation has to be transmitted through an absorbing water layer to the tissue this effect might be an efficient starting mechanism for the generation of a transparent vapor channel. When the fiber tip is in direct contact to the tissue the tensile stresses may help to initiate ablation due to fracture of the tissue material.

Paper Details

Date Published: 10 January 1996
PDF: 11 pages
Proc. SPIE 2624, Laser-Tissue Interaction and Tissue Optics, (10 January 1996); doi: 10.1117/12.229540
Show Author Affiliations
Guenther Paltauf, Karl-Franzens-Univ. Graz (Austria)
Martin Frenz, Univ. Bern (Switzerland)
Heinz Schmidt-Kloiber, Karl-Franzens-Univ. Graz (Austria)

Published in SPIE Proceedings Vol. 2624:
Laser-Tissue Interaction and Tissue Optics
Guy P. Delacretaz; Rudolf W. Steiner; Lars Othar Svaasand; Hansjoerg Albrecht; Thomas H. Meier, Editor(s)

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