Characterization of water contribution to excimer laser ablation of collagen

In order to gain an obvious insight into the role of water in the mechanism of the excimer laser ablation of the cornea, we have macroscopically inves tigated the ablation behavior of collagen gel in the swelled state by direc t photoetching using an ArF excimer laser with time-resolved photography, a nd furthermore, the thermal effects on the microscopic structures of the co llagen molecules by FTIR-ATR spectroscopy. The hydrated collagen film (BF) has a smaller threshold fluence than the dried collagen film (DF). From the time-resolved photographs, the ejected materials were detected only for HF . It was predicted that the effect of bubble formation for HF contributes t o the etching. The FTIR-ATR spectroscopic results revealed that the existen ce of the water suppressed the denaturation of the collagen to gelatin on t he surface in the irradiated region. Overall, it was inferred that during t he ablation process for HF the laser energy would be mostly consumed as the latent heat of evaporation of water, that is, the water in the gel matrix would contribute to the suppression of the increment in the temperature in the irradiated region. (C) 2001 Elsevier Science B.V. All rights reserved.