Critical-angle refractometer enhanced by periodic multilayer coating

We present a high-precision technique for determination of the refractive index (RI) of liquids and gases. The technique is based on standard critical-angle refractometry, sensitivity of which is enhanced by deposition of an additional periodic multilayer stack on the interface between a prism and the medium under investigation. We show that this multilayer stack may be designed so that a reflectance change near the critical angle becomes much sharper than the one in the standard refractometers. Test measurements of set of glucose concentrations in the water are presented and baseline noise of 9 × 10−8 RIU/Hz1/2 is attained.