OPTICAL-FIBER METHODS FOR MEASURING THE DIFFUSE REFLECTANCE OF FLUIDS

Incoherent optical fibres are shown to provide a robust and inexpensive alternative to the traditional integrating sphere method for measuring the diffuse reflectance of multiple-scattering fluids. Measurements of the diffuse reflectance R(d) as a function of the sample thickness d are given for a range of polymer latices, using both an integrating sphere and fibres in various configurations. The Kubelka-Munk expression is found to describe closely the d-dependence of R, the fit of data to theory giving the Kubelka-Munk scattering parameter S. Values of S are compared with those calculated from multiple scattering theory, good agreement being found for fibre configurations where the incident and the scattered flux paths are identical or very close. The results suggest that fibre methods could be readily applied to the continuous or industrial on-line measurement of diffuse reflectance.