Easy integrable refractometer for liquids on extended surfaces

Conventional Abbe refractometers are used to determine the refractive index (RI) of liquid samples placed on a prism surface by critical angle evaluation. However, the use of this method is limited to the investigation of fluids in a laboratory environment. With the purpose of monitoring fluids attaching to extended planar surfaces, a different method is required. We present a RI monitoring device for plates of any given geometry. The proposed method can easily be integrated into a variety of applications using the area of interest as a waveguide for optical radiation. The developed refractometer is tested with sucrose solutions of varying RIs ranging from 1.355 68 to 1.430 80 with an LED source at 589 nm. By implementing a calibration method using standardized solutions, the average uncertainty for the RI determination is 1.6 × 10⁻³. Compared to the values measured by a state-of-the-art refractometer, the maximum deviation is 0.13%.