Konopsky V.N.,Alieva E.V.
Critical-angle refractometer enhanced by periodic multilayer coating. // Sensors and Actuators B: Chemical, 2010, V.150, P.794797.

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, which sensitivity 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 more sharp 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.


Fig.1 The sketch of the experimental setup.


Fig.2 The reflection coefficient of the plane wave from the prism with the multilayer coating (solid line for p-polarization), and without any coating (dashed line for p-polarization and dotted line for s-polarization).


Fig.3 The refractometer response to changes in glucose concentration in water. The corresponding glucose concentrations are shown in %(v/v). The measurement time is 1s per point without posterior data averaging or smoothing. The bottom insert: noise of the baseline. The upper insert: the decrease of the solution RI in response to increase of flow velocity from 0.4 mL/min to 1.2 mL/min.