An optical fibre technique for measuring optical absorption by chromophores in the presence of scattering particles

The evanescent radiation field associated with a suitably-prepared silica optical fibre, whereby the outer cladding has been removed and the core immersed in a liquid, has been investigated for its applicability as a device for measuring the spectral absorption of a liquid containing both chromophore and suspended scattering material. It is found that the evanescent radiation field adjacent to the core-liquid boundary interacts with chromophores in a liquid in much the same way as radiation does when directed, unbound, through a cuvette containing the same liquid in an optical spectrophotometer. However, the small penetration depth of the evanescent field, of the order of one micron, results in a sensor which is found to be insensitive to light-scattering particulate matter than was present in the liquid.