Innovative spectroscopy of liquids: a fiber optic supercontinuum source and an integrating sphere for scattering-free absorption measurements

An innovative fiber optic setup for the scattering-free absorption spectroscopy of liquids is presented. It makes use of an integrating sphere that contains the sample under test, coupled to a fiber optic supercontinuum source and to a fiber optic spectrometer. The highly-bright broadband light shining on the sphere's surface is diffusely reflected and collected by the fiber-coupled spectrometric detector. When an absorbing medium is placed in the cavity, a reduction occurs in the radiance of the sphere. The reduction is related to the absorption and volume of the medium, and is independent of non-absorbing objects within it, such as scattering particles. A collection of turbid lubricant oils was considered as a test case for verifying and validating the innovative scheme of diffuse-light absorption spectroscopy. Scattering-free spectra were successfully measured and processed as product fingerprints for the prediction of turbine types and other parameters that indicate oil quality and wear.