Tensile stress generation by optical breakdown in tissue: experimental investigations and numerical simulations

Alfred Vogel; Richard J. Scammon; Robert P. Godwin

doi:10.1117/12.350002

14 June 1999 Tensile stress generation by optical breakdown in tissue: experimental investigations and numerical simulations

Alfred Vogel, Richard J. Scammon, Robert P. Godwin

Author Affiliations +

Proceedings Volume 3601, Laser-Tissue Interaction X: Photochemical, Photothermal, and Photomechanical; (1999) https://doi.org/10.1117/12.350002
Event: BiOS '99 International Biomedical Optics Symposium, 1999, San Jose, CA, United States

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.

Citation Download Citation

Alfred Vogel, Richard J. Scammon, and Robert P. Godwin "Tensile stress generation by optical breakdown in tissue: experimental investigations and numerical simulations", Proc. SPIE 3601, Laser-Tissue Interaction X: Photochemical, Photothermal, and Photomechanical, (14 June 1999); https://doi.org/10.1117/12.350002

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