Abstract: An experimental apparatus is designed to determine the index of refraction of biological tissue using a laser beam and a prism in the familiar to a specular Fresnel reflection method in which the scattering effects are reduced to be disregarded. One of the advantages of the method is its high sensitivity to a small change in refractive index. A flat heater is contacted on the prism and a tiny heat electric couple is hold between a sample and the prism. The refractive indices of several porcine tissues have been measured over a temperature range of 20 to approximately 70 degrees Celsius. The index of refraction keeps stable levels below 36 degrees Celsius and above 60 degrees Celsius, respectively, but increases with an increase in temperature from 36 to 60 degrees Celsius. During a temperature descent after heating, the evolvement of refractive index is determined by the climax of temperature reached. The heating and cooling procedures are irreversible in optical property of tissue. Such results are consistent to the biological observation and can be explained by the cellular response to temperature. A knowledge of these properties is important for tissue optics and laser medicine. !8
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