Measurement Of The Optical Absorption Coefficient Of Water By White-light Interferometry

The optical absorption coefficient of liquid is a key parameter for quantitative analysis inchemistry, pharmaceutics, biomedical and other analytical field. And, among so manymethods to measure the absorption coefficient of liquid, the optical spectrophotometry basedon the Beer-Lambert's law is the most widely used technique. In this technique, in order tomeasure the absorption coefficient of liquid with high sensitivity, it is necessary to employ aset of cells with different optical path length(OPL), which are required for different samples.In this paper, a technique which combined the Michelson white-light interferometer withthe spectrophotometry is proposed. The characteristic property of this technique is using theMichelson white-light interferometer for the precise measurement of the different OPL ofliquids. And experimental equipment can provide the optimal path length to match with thespecific spectral region. The variable-path-length cell can be adjusted in the range of hundredsof millimeters, with the resolution of±1.25μm, which can meet the needs of the mostsituations.The absorption coefficient of water is measured by this technique in the wavelengthregion around1550nm. Good agreement between the data from this paper and that fromliteratures confirms the validity of the experimental design. The influence of the resolution ofvariable-path-length cell on the results is also discussed. Comparing the path-length errorinduced by resolution of variable-path-length cell with the photometric error, we can concludethe results as: in the ultraviolet-visible-near infrared spectral region, the path-length error isso small that it can be ignored and the technique proposed by this paper is adapted tomeasurement; at higher spectral region, the path-length error is becomes intolerable, somespecial techniques are preferred.