A Study on the Measurement of Refractive Index Dispersion of Liquid with the Total Reflection Comparison Method

Based on the principle of total reflection, a method for measuring the refractive index dispersion of liquid with the comparison method is proposed. The basic principle of measuring the refractive index dispersion of liquid with the prism total reflection comparison method is analyzed, and the calculation formula of refractive index dispersion is derived. The analysis indicates that the refractive index dispersion of the liquid to be tested is related to the refractive index dispersion of the standard liquid and the total reflection limit exit angle, which is independent of the refractive index dispersion of the prism. The corresponding experimental light path and system were set up, and the accuracy of the method is proved by comparing the refractive index dispersion with the Abbe refractometer and double prism method. In the experiment, the refractive index dispersion curves of glucose water, Indian ink, polystyrene solution, magenta solution, saliva, sweat and different concentrations of honey solution samples were measured. The refractive index of the same sample decreased with increasing wavelength, and the fitting equation of the dispersion curve of the relevant sample was obtained with the Cauchy dispersion formula. Experiments show that the accuracy of measuring the refractive index of liquid is about 0.000 2. The refractive index of post-meal sweat and saliva was significantly higher than that before meal. The experimental conclusion provides a possible idea for non-invasive detection of blood glucose in diabetes. The proposed method does not need the refractive index and dispersion of the prism, and has the characteristics of simple experimental system, small sample amount, convenient measurement process and high measurement precision and is suitable not only for transparent and weakly absorbing scattering liquid, but also for measuring solid refractive index dispersion.