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%).