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Lam Hiu Fung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2006. / Includes bibliographical references. / Abstracts in English and Chinese. / Abstract --- p.i / Chinese Abstract --- p.ii / Acknowledgement --- p.iii / Table of Content --- p.vi / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Differential refractometry --- p.1 / Chapter 1.2 --- Nature of refractive index --- p.2 / Chapter 1.2.1 --- Concentration dependence of refractive index --- p.3 / Chapter 1.2.2 --- Wavelength dependence of refractive index --- p.4 / Chapter 1.2.3 --- Temperature and pressure dependence of refractive index / Chapter 1.3 --- Types of differential refractometer --- p.6 / Chapter 1.3.1 --- Deflection type / Chapter 1.3.2 --- Fresnel type --- p.7 / Chapter 1.3.3 --- Interferometric type --- p.8 / Chapter 1.4 --- Reference --- p.9 / Chapter Chapter 2 --- A new laser differential refractomter for real-time measurement of refractive index variation / Chapter 2.1 --- Introduction --- p.12 / Chapter 2.2 --- Experiment / Chapter 2.2.1 --- Experimental setup --- p.14 / Chapter 2.2.2 --- Light source / Chapter 2.2.3 --- Thermostatic cuvutte --- p.16 / Chapter 2.2.4 --- Thermoelectric module --- p.18 / Chapter 2.2.5 --- Inlet and outlet --- p.20 / Chapter 2.2.6 --- Position sensitive detector --- p.21 / Chapter 2.3 --- Basic principles of differential refractometer --- p.23 / Chapter 2.4 --- Materials --- p.25 / Chapter 2.5 --- Results and discussion --- p.25 / Chapter 2.5.1 --- Instrument calibration / Chapter 2.5.2 --- Dynamic range of instrument --- p.26 / Chapter 2.5.3 --- "Instrument stability, noise and resolution" --- p.28 / Chapter 2.5.4 --- Specific refractive index increment measurement --- p.31 / Chapter 2.5.5 --- Temperature effect of refractive index increment --- p.35 / Chapter 2.5.6 --- Wavelength effect of refractive index increment / Chapter 2.6 --- Conclusion --- p.36 / Chapter 2.7 --- Reference --- p.37 / Chapter Chapter 3 --- Enzymatic degradation studies of poly(ethylene oxide)- b-poly(ε-caprolactone) copolymer nanoparticles by differential refractometer / Chapter 3.1 --- Abstract / Introduction --- p.38 / Chapter 3.2 --- Experimental --- p.39 / Chapter 3.2.1 --- Material and sample preparation --- p.41 / Chapter 3.2.2 --- Differential refractometer / Chapter 3.2.3 --- Laser light scattering --- p.41 / Results and dicussion --- p.42 / Chapter 3.3 --- Conclusion --- p.43 / Chapter 3.4 --- Acknowledgement --- p.47 / Chapter 3.5 --- References and notes --- p.48 / Chapter 3.6 / Chapter 3.6.1 --- Figures captions --- p.50 / Chapter 3.6.2 --- Table and Figures --- p.55 / Chapter Chapter 4 --- Appendix - Fundamentals of light scattering and instrumentation --- p.56 / Chapter 4.1 --- Static laser light scattering --- p.57 / Chapter 4.2 --- Dynamic light scattering --- p.58 / Chapter 4.3 --- Correlation function profile analysis --- p.60 / Chapter 4.4 --- Molar mass distribution and conformation of polymers --- p.62 / Chapter 4.5 --- Instrumentation --- p.63 / Chapter 4.6 --- Reference --- p.66

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D.Ing. / Most optical fibre-based ambient refractive index sensors (including individual long-period gratings) rely on spectral attributes obtained in transmission. However, a probe refractometer has been proposed that is based on self-interference of a long-period grating (LPG), thus providing reflectance spectra containing the relevant data. This sensor operates as a Michelson interferometer by virtue of the fact that its constituent LPG acts as both a mode converter and coupler. Its construction is such that optical power coupled into the cladding (when light impinges on the LPG) is reflected at a fibre mirror and returns towards the grating, where it is re-coupled into the fundamental guided mode. Since light waves propagating along the core and cladding material of the fibre cavity beyond the LPG experience different optical path lengths (due to differing mode indices), a phase difference exists between these modes upon recombining at the grating location. This causes interference, which is manifested as a characteristic fringe pattern in the sensor’s reflectance spectrum (analogous to that obtained in the transmission of a twin LPG cascade operating as a Mach-Zehnder interferometer). Research was conducted towards implementing a unique method of temperature compensation in this LPG-based Michelson interferometer. Sensing attributes of individual LPGs were investigated first, with specific emphasis on the temperature characteristics of two different types of host fibre. It was found that LPGs manufactured in conventional ATC SMF-28 fibre (previously hydrogen-loaded to inscribe the grating and annealed after fabrication) and B/Ge co-doped PS1500 fibre from Fibercore exhibited temperature characteristics of opposite polarity. This led to the implementation of a compound-cavity Michelson interferometer whose constituent LPG is written in one type of fibre, while a specific length of the other type of fibre is fusion spliced onto the host fibre section. Experiments verified the success of this temperature-compensation technique, which caused a measured reduction in temperature sensitivity of up to in interferometer phase shift. Measurements of the refractive index of the test substance surrounding the cladding material of the Michelson interferometer’s fibre cavity (and not the LPG itself) could therefore be done without being adversely affected by environmental temperature fluctuations. This was demonstrated experimentally by comparing the interferometer’s phase shift – devoid of temperature-induced effects – due to increasing refractive index of the analyte (as a result of escalating temperature) with index of refraction readings from a temperature-controlled Abbe refractometer. Numerical gradients of linear curves fitted to these results differed by two orders of magnitude less than the resolution of readings obtained from an Abbe refractometer – proof of the success of the temperature compensation technique applied in this LPG-based Michelson refractometer.

Refractometry is a means to measure the refractive indices of liquids, gases, and dielectric solids, either isotropic or anisotropic, by observation of light refraction or reflection with a microscope, refractometer or other more specialized equipment. For anisotropic solids, refractometry by total reflection (RTR) is by far the simplest, most rapid, and precise method to determine the refractive indices, provided a polished surface of sufficient size exists. Its precision exceeds that for routine oil immersion techniques but compares less favorably to that for minimum deviation methods. However, minimum deviation requires large crystals and, moreover, specifically oriented prisms, one for each principal refractive index to be measured and, for triclinic crystals, one for each wavelength of measurement. The phenomenon of polarized light reflection from randomly oriented anisotropic materials has been modeled because, only after a complete understanding of these phenomena could the R TR method be automated. The mathematics and physics required for this stem from theories and equations presented in the literature of ellipsometry, polarized light, and physical optics. These were then modified, rewritten, and unified to suit the requirements of R TR. RTR, first used by Wollaston ( l 802a, l 802b ), was later perfected for the measurement of the refractive indices and orientation of biaxial minerals in thin section (Viola l 899a, l 899b, 1902; Comu 1901, 1902). RTR with the Abbe-Pulfrich refractometer yielded refractive indices to a precision of ±0.0002, or better. Later, Smith (1905a, 1905b) introduced a simpler refractometer, now known as the jeweler's refractometer, which had a precision of ±0.001 to ±0.002. This refractometer is still in use by gemologists. During this century familiarity with the early work has declined; thus several recent papers display a lack of knowledge of aspects of R TR which were already documented in the early 1900s. A new automated refractometer, designed by Bloss, has precision of ±0.0002 and will be able to measure the refractive indices and orientation of a biaxial mineral in a petrographic thin section. Even for triclinic crystals, a single polished surface arbitrarily oriented will suffice for measurement of all three principal refractive indices, whatever the wavelength supplied. The design and testing of this refractometer has taken approximately three years. Two prototypes have been built and tested. Results from the second prototype are presented. / Ph. D.

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