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Proceedings Paper

Tensile stress generation by optical breakdown in tissue: experimental investigations and numerical simulations
Author(s): Alfred Vogel; Richard J. Scammon; Robert P. Godwin
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Paper Abstract

Biological tissue is more susceptible to damage from tensile stress than to compressive stress. Tensile stress may arise through the thermoplastic response of laser-irradiated media. Optical breakdown, however, has to date been exclusively associated with compressive stress. We show that this is appropriate for water, but not for tissues for which the elastic-plastic material response needs to be considered. The acoustic transients follow optical breakdown in water and cornea were measured with a fast hydrophone and the cavitation bubble dynamics, which is closely linked to the stress wave generation, was documented by flash photography. Breakdown in water produced a monopolar acoustic signal and a bubble oscillation in which the expansion and collapse phases were symmetric. Breakdown in cornea produced a bipolar acoustic signal coupled with a pronounced shortening of the bubble expansion phase and a considerable prolongation of its collapse phase. The tensile stress wave is related to the abrupt end of the bubble expansion. Numerical simulations using the MESA-2D code were performed assuming elastic-plastic material behavior in a wide range of values for the shear modulus and yield strength. The calculations revealed that consideration of the elastic-plastic material response is essential to reproduce the experimentally observed bipolar stress waves. The tensile stress evolves during the outward propagation of the acoustic transient and reaches an amplitude of 30 - 40% of the compressive pulse.

Paper Details

Date Published: 14 June 1999
PDF: 16 pages
Proc. SPIE 3601, Laser-Tissue Interaction X: Photochemical, Photothermal, and Photomechanical, (14 June 1999); doi: 10.1117/12.350002
Show Author Affiliations
Alfred Vogel, Medizinisches Laserzentrum Luebeck GmbH (Germany)
Richard J. Scammon, Los Alamos National Lab. (United States)
Robert P. Godwin, Los Alamos National Lab. (United States)

Published in SPIE Proceedings Vol. 3601:
Laser-Tissue Interaction X: Photochemical, Photothermal, and Photomechanical
Steven L. Jacques; David H. Sliney; Gerhard J. Mueller; Gerhard J. Mueller; Andre Roggan; Andre Roggan; David H. Sliney, Editor(s)

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