Photoablation with the free-electron laser in the far IR in biological soft tissue (cornea)

Abstract

Wavelengths in the range from 12 micrometers up to 70 micrometers (far IR) have a water absorption coefficient in the same order as wavelengths used successfully for ablation near the 6 micrometers water absorption peak. Thus these wavelengths were considered to allow effective photothermal ablation of biological materials. The Free-Electron Laser (FEL) in Nieuwegein, NL (FELIX) is capable of delivering (far) IR laser light between 6 micrometers and 110 micrometers and was used for the first systematic investigation of the ablation quality (ablation depth per pulse and collateral damage beyond the surface) in the wavelength range between 12 micrometers and 70 micrometers . Porcine cadaver corneas were used as target material. Ablation depth per pulse as well as collateral thermal damage (extension of eosinophilic zone beyond the irradiated surface) were measured by histologic micrometry. It was found that the applied IR laser light can be used for an effective ablation of biological materials with a high water content. The experimental data are compared with theoretical values according to a previously described model for photoablation.