Combined effect of IR and UV laser radiation on biological tissues: cleaning

The objective of the present communication is the investigation of the successive effect of IR and UV laser pulses on biological tissue. As examples of tissues the authors use human lenses from individuals suffering from cataracts and porcine cornea, both of them in vitro. In the experiments, the authors use the laser radiation of different wavelengths with different values of water absorption coefficients /spl alpha/: a YAG:Er laser with wavelength /spl lambda/=2.94 /spl mu/m (/spl alpha//spl sim/10/sup 4/ cm/sup -1/), a KGSS:Er laser with /spl lambda/=1.54 /spl mu/m (/spl alpha//spl sim/10 cm/sup -1/), and YAG:Nd lasers with /spl lambda/=1.32 /spl mu/m (/spl alpha//spl sim/1 cm/sup -1/) and /spl lambda/=1.44 /spl mu/m (/spl alpha//spl sim/30 cm/sup -1/) operating in free-running mode. As a source of UV laser radiation, the authors use the fifth harmonic of a Nd:YAP laser with wavelength of 216 nm and pulse energy up to 10 mJ. The pulse-to-pulse kinetics of laser ablation and modifications is followed by optical coherence tomography (OCT). The final results are compared with the histological data, The quality of laser ablation may be characterized by the size of the thermally damaged zone adjacent to the surface of ablation crater. The authors show that it is possible to create ablation crater mainly by the IR radiation. Then, the UV radiation, which is absorbed by collagen chromophores, can be used to clean the surfaces of ablation crater due to elimination of damaged layers that remain after IR irradiation. Theoretical estimations are performed to understand the confinement of the effect of UV radiation within the damaged layers. The authors also report the first experimental results obtained on simultaneous IR and UV irradiation of biological tissues.