The understanding of tissue ablation by pulsed lasers is important for the development of medical applications of these devices. It has long been assumed that absorption of the laser radiation can be described by a constant absorption coefficient. The literature, however, clearly indicates that IR and UV absorption of a major tissue constituent, water, changes as a function of the chemical environment in which the water is found. For example, the absorption by water changes with temperature. Our preliminary data show the importance of a changing absorption coefficient on infrared absorption. We propose to explore those factors that cause changes in UV and 1R absorption in tissue and relate these changes to the tissue ablation process. We propose a series of experimental procedures and the further development of an ablation model to help guide and interpret the experimental results. We propose the spectroscopic study of water and electrolyte solutions; such studies form the basis by which to understand the absorption by tissue of light. We will extend the initial studies to the spectroscopy of soft and hard tissues. As opposed to previous spectroscopic studies of tissue, we will concentrate upon the effect of temperature and ion concentration. Spectroscopy with low intensity light will be followed by pump-probe spectroscopy using high intensity pump beams. Ablation studies will involve the measurement of plume parameters, cutting rate, and shock wave production. The ablation studies are designed to verify and augment the spectroscopic studies. An ablation model based upon dynamically changing absorption coefficients as well as thermodynamic equations of state will be used to understand the effects of superheating and ablation of tissue.
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