Austin, Edward Alfred Denzil
Studies of measurement techniques for indirect chemical sensing based on fluorescence spectroscopy and applications for fibre-optic sensors.
University of Southampton, Optoelectronic Research Centre,
This thesis describes experimental and theoretical studies of interrogation systems for
determining fluorescent decays of order a few microseconds. The studies have enabled
optimised design of interrogators for sensing oxygen using a fluorescent polymerencapsulated
ruthenium complex. Two basic interrogation methods were explored, using
blue LED excitation.
The Rapid Lifetime Detection (RLD) scheme, a fluorescence interrogation method based
on direct interrogation of the decay curve following pulsed excitation was generalised, and
a novel method for optimising measurement precision derived. The effect of background
light on the optimum was quantified. Dissolved (aqueous) oxygen concentration was
measured to a precision of 1 part per billion using a 1 second response time (the peak
fluorescence power was only 12.5±0.5pW).
A second interrogation method, where the phase delay between an intensity modulated
excitation source and the resultant fluorescence is processed to make measurements, was
for the first time, fully analysed for measurement of exponential decays. When measuring
fluorescence lifetimes in the range 2.9-3.3?s, a precision of 2.3 x 10-10 s Hz-0.5 was
achieved. (The peak fluorescence power was 500±25pW).
A novel combination of ruby optical temperature sensor insert and oxygen sensing layer
was demonstrated as a simultaneous temperature and oxygen sensor.
A new fluorescence calibration standard consisting of thermally stabilised titanium-dopedsapphire
sample was constructed to calibrate and test the indicators.
This work was sponsored by a BRITE EuRam European project, which helped determine
the priorities of the research.
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