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Proceedings Paper

Mechanical response of agar gel irradiated with Nd:YAG nanosecond laser pulses
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Paper Abstract

Nanosecond long laser pulses are used in medical applications where precise tissue ablation with minimal thermal and mechanical collateral damage is required. When a laser pulse is incident on a material, optical energy will be absorbed by a combination of linear and nonlinear absorption according to both: laser light intensity and material properties. In the case of water or gels, the first results in heat generation and thermoelastic expansion; while the second results in an expanding plasma formation that launches a shock wave and a cavitation/boiling bubble. Plasma formation due to nonlinear absorption of nanosecond laser pulses is originated by a combination of multiphoton ionization and thermionic emission of free electrons, which is enhanced when the material has high linear absorption coefficient. In this work, we present measurements of pressure transients originated when 6 ns laser pulses are incident on agar gels with varying linear absorption coefficient, mechanical properties and irradiation geometry using laser radiant exposures above threshold for bubble formation. The underlying hypothesis is that pressure transients are composed of the superposition of both: shock wave originated by hot expanding plasma resulting from nonlinear absorption of optical energy and, thermoelastic expansion originated by heat generation due to linear absorption of optical energy. The objective of this work is to evaluate the relative contribution of each absorption mechanism to mechanical effects in agar gel. Real time pressure transients are recorded with PVDF piezoelectric sensors and time-resilved imaging from 50 μm to 10 mm away from focal point.

Paper Details

Date Published: 23 February 2010
PDF: 9 pages
Proc. SPIE 7562, Optical Interactions with Tissues and Cells XXI, 756212 (23 February 2010); doi: 10.1117/12.841476
Show Author Affiliations
Francisco G. Pérez-Gutiérrez, Univ. of California, Riverside (United States)
Rodger Evans, Ctr. de Investigación Científica y de Educación Superior de Ensenada (Mexico)
Santiago Camacho-López, Ctr. de Investigación Científica y de Educación Superior de Ensenada (Mexico)
Guillermo Aguilar, Univ. of California, Riverside (United States)

Published in SPIE Proceedings Vol. 7562:
Optical Interactions with Tissues and Cells XXI
E. Duco Jansen; Robert J. Thomas, Editor(s)

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