Anomalous Optical Properties of Water at 40°C and 1.06µm

Abstract

The temperature dependency of the optical properties of water plays an important role in understanding laser-tissue and laser-bacteria interactions. Recent interests in laser inactivation or sterilization [1,2] have shown that lasers offer specific advantages over conventional sterilization techniques, for example, autoclaves. The laser sterilization mechanism has not yet been elucidated, however, but it is clear that the mechanism will be wavelength dependent. With excimer lasers, operating in the UV, it is likely to be the normal UV sterilization process (254-260nm) in which thymine dimers inhibit correct replication of the DNA during the cell's reproduction. Lasers operating in the IR (Nd:YAG, CO2) have been shown to exhibit a bactericidal capacity. This mechanism is probably partly thermal. Present efforts to model the interaction of the laser radiation and bacteria have been hindered by the availability of suitable data. To overcome this problem, the present work was initiated to determine the temperature dependency of the absorption and scattering coefficients of water, the principal constituent of bacteria, and used to develop models of the laser sterilization process for the Nd:YAG laser operating at 1.06µm.