A simple method based on total internal reflection is presented for measuring the refractive index of biological tissue. A narrow laser beam and a semicylindrical lens in contact with a tissue specimen are used in the experimental apparatus. The dependence of the internal reflectivity on the angle of incidence is measured to determine the critical angle and therefore the refractive index of tissue. The experimental results for several tissue samples show that the method is reliable and useful for studying tissue optics. The principal advantages of the method are its elimination of scattering effects, suitability to a small in vitro sample, and excellent accuracy.
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