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Proceedings Paper

Influence of pulse width and speckle formation on the ablation thresholds in water by means of pulsed mid-IR laser radiation
Author(s): Christoph Hansen; Ralf Brinkmann; Reginald Birngruber
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Paper Abstract

The evaporation of water by means of fiber guided pulsed mid- infrared laser radiation was investigated. The influence of the pulse duration and speckle formation on the ablation threshold was determined. Optical on-line monitoring of refractive index changes at the distal fiber tip has been used to determine the cavitation threshold. Temporal and spatial speckle pattern at the distal application fiber tip were measured by imaging the fiber tip to a reference plane. An IR- CCD camera and fast IR-photodiodes were used to monitor the intensity modulation. The measured cavitation thresholds show a strong dependence on the pulse energy and the pulse duration. Overheating of water at the evaporation threshold could be calculated for the Q-switched pulse mode. Regarding speckle, spatial peak intensities up to a factor of 1.5 and 2.6 over the average intensity were evaluated for the Q- switched and the free running mode, respectively. Speckle modulation plays an important role in the free running mode to achieve the boiling point of water with the threshold radiant exposure determined. Furthermore, transient intensity fluctuations were measured across the beam profile at the fiber tip.

Paper Details

Date Published: 14 January 1998
PDF: 6 pages
Proc. SPIE 3195, Laser-Tissue Interaction, Tissue Optics, and Laser Welding III, (14 January 1998); doi: 10.1117/12.297901
Show Author Affiliations
Christoph Hansen, Medical Laser Ctr. Luebeck GmbH (Germany)
Ralf Brinkmann, Medical Laser Ctr. Luebeck GmbH (Germany)
Reginald Birngruber, Medical Laser Ctr. Luebeck GmbH (Germany)

Published in SPIE Proceedings Vol. 3195:
Laser-Tissue Interaction, Tissue Optics, and Laser Welding III
Guy P. Delacretaz; Guilhem Godlewski M.D.; Roberto Pini; Rudolf W. Steiner; Lars Othar Svaasand, Editor(s)

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