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Fibre optic fluorescence thermometry

Zhang, Z. Y. (1993). Fibre optic fluorescence thermometry. (Unpublished Doctoral thesis, City, University of London)

Abstract

Starting with a review of the development of fibre optic temperature sensing techniques, this thesis is comprised of the author’s work on the fibre optic fluorescence thermometry, a prominent branch of fibre optic thermometry. First, the temperature dependences of fluorescence in Cr3+ doped materials, a large family of promising temperature sensing materials are examined, which lay the theoretical basis of the fluorescence thermometry discussed herein. Based on the Tanabe-Sugano diagram, such temperature dependences are characterised with the crystal field strengths of the host materials and two single configurational coordinate models are proposed for the temperature dependences in materials with high and low crystal field strengths respectively. These models have successfully explained the great diversity in the temperature dependences of the Cr3+ fluorescence lifetimes, by their close fits to the experimental data of various corresponding materials.

Then, the work contributing to the instrumentation aspects of the fluorescence thermometry is discussed. Evolving from the lock-in amplifier technique, a category of novel, effective and versatile instrumentation approaches: the phase-locked detection of fluorescence lifetimes (PLD), is presented. The operating principles of these new signal processing approaches are described with theoretical analysis and graphic illustrations. The theoretical basis of the electronic design is provided.

After the descriptions of the PLD techniques, examples of their applications in various successful Cr3+fluorescence based fibre optic thermometer schemes are presented, which are developed in the course of this study. These demonstrate that the PLD schemes can be operated over a wide consecutive measurement range of fluorescence lifetime with a high measurement resolution, and are particularly useful for temperature sensor applications using long lifetime (> 1 fis) fluorescent media. Some considerations in relation to specific applications, e.g. in high temperature sensing or in medical RF hyperthermia treatment, are discussed including the fabrications of temperature fibre probes for various specified applications. The applications of the two single configurational coordinate models proposed in this work are also discussed showing their good potentials for the calibration of the Cr3+ fluorescence based thermometers.

Finally, the feasibility of the incorporation of the fluorescence thermometry with the long-established radiation thermometry, to extending the measurement range of a fibre optic temperature sensor is illustrated, by a fibre optic sensor scheme based the cross referencing between the fluorescence lifetime of Nd:YAG and the blackbody radiation at a single wavelength, 1064 nm. To conclude this thesis, a cross comparison to previous experimental work is made with a discussion of the future work, and the further potentials of this work are also investigated.

Publication Type: Thesis (Doctoral)
Subjects: T Technology > TA Engineering (General). Civil engineering (General)
Departments: School of Science & Technology > Engineering
School of Science & Technology > School of Science & Technology Doctoral Theses
Doctoral Theses
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