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Journal of Biomedical Optics

Photoablation with the free-electron laser between 10 and 15 um in biological soft tissue (cornea)
Author(s): Rudolf Walker; Manfred Ostertag; Alexander F. G. van der Meer; Thomas Bende; Karl C. Schmiedt; Benedikt J. Jean
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Paper Abstract

The ablation depth and collateral thermal damage for pulsed infrared photoablation as a function of wavelength with the free-electron laser (FEL) at 10.1, 11.8, 12.8, and 14.5 mm wavelengths is investigated. FEL data are compared with the blow-off and the continuous ablation models. Porcine cadaver corneas were used as target material. [Ablation depth per pulse as well as collateral thermal damage (extension of eosinophilic zone at the excision base beyond the irradiated surface) were measured by histologic micrometry.] The experimental data are compared with theoretical calculations for both models. At low water absorption (10.1 mm) the additional absorption of the cornea was taken into account. FEL data were: energy per pulse between 15.6 and 17.8 mJ, ablation zone around 0.2 mm2, and pulse length 4 ms (macropulse). In this wavelength range an effective photoablation of biological materials with a high water content can be achieved. The measured FEL data of ablation depth fail to confirm the blow-off model; they are 3 to 5 times higher than predicted. However, they are in agreement with the continuous ablation model, describing ablation depth sufficiently well (610%). The wavelength range from 11.8 to 14.5 mm is dominated by water absorption; here the ablation depth depends on the water absorption coefficient only, if other parameters are kept constant. At a 10.1 mm wavelength, collagen absorption contributes to the overall absorption of corneal tissue. The ablation depth can only be described by the continuous ablation model; however, the collateral thermal damage pattern can be described by both models (deviation of data 610–25%).

Paper Details

Date Published: 2 April 1997
PDF: 7 pages
J. Biomed. Opt. 2(2) doi: 10.1117/12.268951
Published in: Journal of Biomedical Optics Volume 2, Issue 2
Show Author Affiliations
Rudolf Walker, Univ. Tuebingen (Germany)
Manfred Ostertag, Univ. Tuebingen (Germany)
Alexander F. G. van der Meer, FOM - Institute for Plasma Physics (Netherlands)
Thomas Bende, Univ. Tuebingen (Germany)
Karl C. Schmiedt, Univ. Eye Hospital (Germany)
Benedikt J. Jean, Univ. Tuebingen (Germany)

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