Refractive index measurement for biomaterial samples by total internal reflection

The refractive index of biological tissue is a fundamental parameter in applications of optical diagnosis and laser treatments. In the present work, the refractive indices and thermo-optic coefficients of some basic biomaterials, such as blood plasma, haemoglobin solution and lipid membrane, were studied by the method of total internal reflection at the wavelengths of 532 and 632.8 nm that are the most frequently used laser wavelengths in the biomedical field. The effects of the sample concentration and the temperature on refractive index were measured, and empirical relationships were summarized, accompanied by a theoretical explanation based on molecular polarization theory. The results provide some fundamental data for the refractive indices of these biomaterials under variant conditions, and also demonstrate that the total internal reflection method is a feasible and reliable way to measure the refractive indices of biological samples.