Role of wavelength and pulse structure in the ablation of tissue and gelatin.

摘要

The goal of these measurements has been to investigate the wavelength dependence of infrared laser induced tissue ablation. Fourier transform infrared spectroscopy of tissues guided the selection of wavelengths to which the Vanderbilt Free-Electron Laser (FEL) was tuned in order to study ablation rates and residual thermal damage in tissues including neural, ocular and dermal. Targeting FEL radiation to the amide II mode of proteins leads to tissue ablation characterized by minimal collateral damage while maintaining a substantial ablation rate. To account for these observations, a novel ablation mechanism has been proposed based on compromising tissue through resonant denaturation of structural proteins, which was tested using dynamic measurements on mechanical (ns) time scales of ablation of gelatin by FEL radiation. Simultaneous measurements of ejected material using a continuous HeNe probe beam tangential to the gelatin surface and the concomitant stress wave in the bulk of the sample provide an intriguing dynamical picture of the ablation event generated by infrared radiation of different wavelengths and different macropulse durations. By varying the macropulse duration from 60 to 200 ns with a broadband infrared Pockels cell, it is evident in both ejecta data and the stress transient data that the bulk of the ablation occurs after the end of the laser pulse. The most significant difference between ablation induced by different laser wavelengths, however, appears during the laser pulse, at the onset of ablation.