DIFFUSE-LIGHT ABSORPTION SPECTROSCOPY BY MEANS OF A FIBER OPTIC SUPERCONTINUUM SOURCE - AN INNOVATIVE TECHNIQUE -

Absorption spectroscopy in the visible and near infrared spectral ranges is one of the most popular methods in conventional analytical chemistry. Diffuse-light absorption spectroscopy is an original technique for liquid analysis, which overcomes turbidity dependency of conventional absorption spectroscopy. It makes use of an integrating sphere, containing the sample under test, coupled to a source and to a detector. When a light source is coupled to the integrating sphere, all light shining on the sphere surface is diffusely reflected, and a detector can be placed anywhere in the sphere to gather the average flux. By inserting an absorbing medium in the cavity, a reduction of the radiance in the sphere occurs. The reduction is related to the absorption of the medium and to its volume, and is independent of non-absorbing objects within it, like turbidity. This paper shows the results of an original test of diffuse-light absorption spectroscopy. A supercontinuum fiber optic source was used for characterizing a collection of lubricant oils of different turbine types. Multivariate processing of spectral data made it possible to achieve a turbidity independent oil condition monitoring.