Improved probe geometry for fluorescence-based fibre-optic temperature sensor

A fluorescent fibre probe with high collection efficiency for fluorescence-lifetime measurements is presented. A numerical model for calculating the collection efficiency for different probe designs has been employed. The position and number of fibres, crystal geometry, crystal-fibre gap and the backside crystal reflectivity are used as evaluation parameters for probe optimization. A possible three-fold increase in collected fluorescent light intensity is predicted in comparison with the classical two-fibre configuration. The model has been confirmed by constructing a seven-fibre probe with alexandrite crystal as the sensing element. An accuracy of +/- 0.3 K is achieved in the 20-90 degrees C temperature range.