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Nonlinear-optical spectroscopy for tissue diagnostics: application to laser ablation of skin tissue

Tissue nonlinear spectroscopy has been investigated as potential method for the monitoring of the laser ablation process of skin tissues. Nonlinear optical phenomenon of second harmonic generation that effectively occurs when femtosecond-picosecond duration pulses of laser irradiation passed through collagen contained layer is used to monitor photothermal processes. The samples of skin tissues were irradiated by continuous wave Nd:YAG laser and then were tested by probing picosecond beam. The change in amplitude of nonlinear optical response at ablated area of sample has been revealed. As result of laser ablation in 2mm of diameter area the SHG nonlinear signal was increased approximately two times. Polarization dependence of second harmonic generation has been studied, comparing with another nonlinear process - two-photon fluorescence in samples of ordered biotissue.