title: Inverse Abbe-method for observing small refractive index changes in liquids.
abstract: This study concerns an optical method for the detection of minuscule refractive index changes in the liquid phase. The proposed method reverses the operation of the traditional Abbe refractometer and thus utilizes the light dispersion properties of materials, i.e. it involves the dependence of the refractive index on light wavelength. In practice, the method includes the detection of light reflection spectra in the visible spectral range. This inverse Abbe method is suitable for liquid quality studies e.g. for monitoring water purity. Tests have shown that the method reveals less than per mil NaCl or ethanol concentrations in water.
authors.affiliation: University of Oulu, Cemis-Oulu, Technology Park, PO Box 127, FI-87400 Kajaani, Finland. Electronic address: jukka.raty@oulu.fi.
authors.forename: Jukka
authors.initials: J
authors.lastname: Räty
authors.affiliation: Institute of Photonics, University of Eastern Finland, PO Box 111, FI-80101 Joensuu, Finland.
authors.forename: Kai-Erik
authors.initials: KE
authors.lastname: Peiponen
keywords: Abbe refractometer; Inverse Abbe method; Light dispersion; Reflection spectrum; Refractive index; Water purity