Photoablation with the free-electron laser between 10 and 15 um in biological soft tissue (cornea)

Rudolf Walker; Manfred Ostertag; Alexander F. G. van der Meer; Thomas Bende; Karl C. Schmiedt; Benedikt J. Jean M.D.

doi:10.1117/12.268951

1 April 1997 Photoablation with the free-electron laser between 10 and 15 um in biological soft tissue (cornea)

Rudolf Walker, Manfred Ostertag, Alexander F. G. van der Meer, Thomas Bende, Karl C. Schmiedt, Benedikt J. Jean M.D.

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Journal of Biomedical Optics, Vol. 2, Issue 2, (April 1997). https://doi.org/10.1117/12.268951

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%).

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Rudolf Walker, Manfred Ostertag, Alexander F. G. van der Meer, Thomas Bende, Karl C. Schmiedt, and Benedikt J. Jean M.D. "Photoablation with the free-electron laser between 10 and 15 um in biological soft tissue (cornea)," Journal of Biomedical Optics 2(2), (1 April 1997). https://doi.org/10.1117/12.268951

Published: 1 April 1997

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