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We have modified a recently developed reflectometer so that surface plasmon resonance (SPR) sensing is now possible. Thus, the complex refractive index of liquids can be obtained at a desired wavelength (the existing setup allows the use of the visible-NIR spectral range) using both the SPR and conventional measurement modes of the reflectometer. The multifunction operation of the present apparatus offers possibilities for off- and on-line industrial inspection of liquids.

The reflectance from industrial pulping solutions was investigated with the use of a reflectometer. It was observed that the reflectance is time-dependent on the contamination of the probe window. The optical constants of the pulping solutions were calculated by using Fresnel's theory and the concept of critical angle. A simple mathematical model, based on the random contamination of the probe window, was observed to yield satisfactory agreement between the measurement and theory of reflectance. It is proposed that optical constants of pulping solutions can be estimated despite the contaminated layer on the prism face.