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Proceedings Paper

Computational modeling of stress transient and bubble evolution in short-pulse laser-irradiated melanosome particles
Author(s): Moshe Strauss; Peter A. Amendt; Richard A. London; Duncan J. Maitland; Michael E. Glinsky; Charles P. Lin; Michael W. Kelly
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Paper Abstract

Laser injury by sub-nanosecond pulses in the eye and skin is related to strongly absorbing pigment particles such as melanin with dimension of order 10-15 nm. Single melanosomes, with size of approximately 1 micrometers and containing many such melanin particles, were isolated in water and irradiated with 100 psec pulses. Using time resolved imaging techniques, they observed the emission of a strong shock wave followed by rapid bubble expansion on a nanosecond timescale. The shock had a supersonic speed of approximately 2700 m/sec and an initial pressure of nearly 35 kbars. The shock wave can induce further tissue damage in addition to that produced by the bubble expansion and reduce the threshold for laser damage in the retina. In this work we simulate the system by using the hydrodynamic computer code LATIS with a realistic equation of state for water. We simulate both isolated melanin particles and whole melanosomes. Our melanosome model considers a spherical structure of order 1 micrometers in diameter with a uniform energy. This is consistent with the fact that the melanin particles are not stress confined while the melanosome is almost stress confined; thus, the pressure builds up uniformly in the melanosome. The details of the dynamics of the supersonic shock wave emission and rapid bubble evolution on both the melanin and melanosome scales are investigated. Comparison between modeling and experiments is presented. In order to achieve peak pressures and shock speeds comparable to the reported values, it is necessary to model the melanosome as having an absorption coefficient of approximately 6000 cm-1. Another way to achieve agreement with experiment is if the superposition of shock waves from the many melanin particles inside the melanosome produces a stronger shock than calculated by assuming a smooth absorption, as in our melanosome model. A better experimental determination of the values of linear and non- linear absorption coefficients for a single melanosome is needed in order to decide between the two approaches.

Paper Details

Date Published: 16 June 1997
PDF: 10 pages
Proc. SPIE 2975, Laser-Tissue Interaction VIII, (16 June 1997); doi: 10.1117/12.275491
Show Author Affiliations
Moshe Strauss, Nuclear Research Ctr. and Univ. of California/Davis (Israel)
Peter A. Amendt, Lawrence Livermore National Lab. (United States)
Richard A. London, Lawrence Livermore National Lab. (United States)
Duncan J. Maitland, Lawrence Livermore National Lab. (United States)
Michael E. Glinsky, Lawrence Livermore National Lab. (United States)
Charles P. Lin, Wellman Labs. of Photomedicine, Massachusetts General Hospital, and Harvard Medical School (United States)
Michael W. Kelly, Wellman Labs. of Photomedicine, Massachusetts General Hospital, and Harvard Medical School (United States)

Published in SPIE Proceedings Vol. 2975:
Laser-Tissue Interaction VIII
Steven L. Jacques, Editor(s)

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