Miniature isotropic optical fibre probes for quantitative light dosimetry in tissue

A small detector to measure light fluence rates in turbid media and biological tissue, based on an optical fibre with a fluorescent dye-doped tip, is presented. The measured optical power of the fluorescent light transmitted through the fibre is directly proportional to the local fluence rate of the treatment or excitation light at the tip. The detector has been built as small as 170 microns outer diameter, while retaining good mechanical properties for insertion into soft tissue. The detector response is linear with fluence rate over a wide range and isotropic for all angles less than 160 degrees from the forward direction. Hence, the detector can measure accurately the fluence rate in turbid media and biological tissue. This fluorescent tip design has no fundamental restrictions in size and shows comparable isotropy, but is less sensitive than, fluence rate detectors based on optical fibres with light-scattering tips.