by Jim Tsz Fung. / Thesis submitted in 1998. / Thesis (M.Phil.)--Chinese University of Hong Kong, 1999. / Includes bibliographical references. / Abstract also in Chinese. / Abstract --- p.i / Abstract(Chinese) --- p.iii / Acknowledgment --- p.iv / Contents --- p.v / Abbreviations --- p.vii / List of Figures --- p.xi / List of Tables --- p.xvi / Chapter 1. --- Introduction --- p.1 / Chapter 2. --- Theoretical background and instrumentation --- p.8 / Chapter 2.1 --- Static laser light scattering --- p.9 / Chapter 2.2 --- Dynamic laser light scattering --- p.10 / Chapter 2.3 --- Laser light scattering instrumentation --- p.11 / Chapter 2.4 --- Refractive index increment measurement --- p.13 / Chapter 2.5 --- The principle of steady-state fluorescence spectroscopy --- p.14 / Chapter 2.5.1 --- Solvent effects on fluorescence emission --- p.17 / Chapter 2.5.2 --- Excimer --- p.17 / Chapter 2.5.3 --- Characterization of fluorescence emission spectra of pyrene --- p.18 / Chapter 2.6 --- Polymer micronization --- p.20 / Chapter 2.7 --- Enzyme purification --- p.22 / Chapter 3. --- Laser light-scattering study of enzymatic biodegradation of poly(ε-caprolactone) --- p.25 / Chapter 3.1 --- A novel laser light scattering study of enzymatic biodegradation of PCL nanoparticles --- p.26 / Chapter 3.2 --- A modified heterogeneous kinetics for the enzymatic biodegradation of poly(s-caprolactone) in aqueous solution --- p.42 / Chapter 4. --- Laser light-scattering study of enzymatic biodegradation of poly(ethylene oxide-b-ε-caprolactone) diblock copolymer --- p.59 / Chapter 4.1 --- Enzymatic biodegradation of poly(ethylene oxide-b-ε- caprolactone) diblock copolymer and its potential biomedical applications --- p.60 / Chapter A1. --- Static laser light scattering --- p.80 / Chapter A2. --- Dynamic laser light scattering --- p.85

[pt] O presente trabalho tem por objetivo implantar um método para calibração de sistema de medição linear por interferometria laser por meio de comparação a um outro sistema laser de referência. O referido método é considerado mais simples que a calibração por componentes realizada atualmente e, conforme demonstrado no trabalho, apresenta confiabilidade metrológica que atende a exatidão necessária para as aplicações dos laseres em metrologia dimensional, vindo suprir uma necessidade metrológica dos laboratórios credenciados pelo Instituto Nacional de Metrologia, Normalização e Qualidade Industrial (Inmetro) e do parque industrial brasileiro, usuários destes sistemas de medição. A implantação do sistema para calibração de lasers de medição foi baseada em normas internacionais de calibração e de cálculo da incerteza de medição e utilizou um sistema laser de referência calibrado no Inmetro, com rastreabilidade a padrões nacionais, com as menores incertezas possíveis. O método de medição implantado realiza a calibração de um sistema laser por comparação a outro utilizando medições feitas a partir do deslocamento da mesa onde é a apoiado o prisma óptico. O que é de fato analisado é a diferença das medições dos dois sistemas laser para um mesmo deslocamento. Foram registradas as diferenças das indicações de 200 mm em 200 mm de deslocamento, em um total de 2000 mm, que variaram de 0,027 µm a 0,690 µm. Foram realizadas três medições para cada deslocamento e quatro repetições completas do procedimento em dias diferentes, com variação do desvio padrão de 0,009 µm a 0,098 µm e incertezas expandidas que variaram de 0,109 µm a 0,306 µm. São apresentadas a metodologia de calibração, cálculos das correções, fontes de erros e cálculos da incerteza de medição para a comparação de sistemas laseres de medição linear. / [en] The present work aims at the implementation of a calibration method for interferometric linear laser measurement systems by comparison to another reference system. The proposed method is considered simpler than the calibration by components that is carried out today at Inmetro (National Institute of Metrology, Standardization and Industrial Quality) and, as demonstrated along this work, presents the metrological reliability and accuracy necessary for several applications of lasers in dimensional metrology. This approach will supply the metrological needs of several laboratories accredited by Inmetro and of the Brazilian industry in general, users of such measurement systems, regarding cost and time of calibration. The method implemented was based on international technical standards related to calibration and uncertainty calculation and used a reference system calibrated at Inmetro, with traceability to national standards, with the lowest uncertainties that could be achieved. The said method performs the calibration of a laser system by comparison to another through measurements of the displacement of the table where the optical prism rests. What is indeed analyzed is the difference of the measurements obtained by the two laser systems for the same table displacement. The differences were recorded for each displacement of 200 mm, in a total of 2,000 mm, their variation being from 0.027 µm to 0.690 µm. The whole procedure was repeated four times, in different days, with three measurements for each displacement. Their standard deviation varied from 0.009 µm to 0.098 µm while their expanded uncertainties varied from 0.109 µm to 0.306 µm depending on the value of the displacement. The calibration methodology, correction calculation, errors sources and measurement uncertainty calculations for the linear measurement laser systems comparison are presented in this dissertation.

O objetivo do presente estudo foi avaliar in situ o efeito da associação do verniz fluoretado ao laser de Er:YAG e ao laser Nd:YAG na permeabilidade da dentina radicular erodida. Quarenta e oito fragmentos de dentina radicular bovina, com dimensões 2x2x2 mm, foram submetidos a um desafio erosivo inicial com ácido cítrico (0,3%, pH 3,2), por duas horas, sob agitação e armazenados em saliva artificial por vinte e quatro horas. Posteriormente, os espécimes foram divididos em relação aos tratamentos: verniz fluoretado e não fluoretado e subdivididos conforme a irradiação: laser de Er:YAG (100mJ, 3Hz), laser de Nd:YAG (70mJ, 15 Hz) e não irradiado. Após um período de lead in (2 dias), os voluntários (n=8) utilizaram dispositivos palatinos contendo três espécimes que foram submetidos a desafios erosivos ex vivo, quatro vezes ao dia, com ácido cítrico (0,3%, pH 3,2), durante 90s, por cinco dias. Na primeira fase do experimento, metade dos voluntários utilizou dispositivos contendo fragmentos tratados com verniz fluoretado, verniz fluoretado + laser de Er:YAG e verniz fluoretado + laser de Nd:YAG. A outra metade utilizou verniz não fluoretado, verniz não fluoretado + laser de Er:YAG e verniz não fluoretado + laser de Nd:YAG. Depois de um período de wash-out (15 dias), os voluntários foram cruzados quanto aos tratamentos, caracterizando um experimento cross-over 2x2. Ao final de cada fase experimental, a permeabilidade dentinária foi avaliada. A ANOVA dois critérios e o teste complementar de Duncan revelaram uma diferença significativa entre os espécimes tratados com o verniz fluoretado (p=0,005), verniz fluoretado + laser de Er:YAG (p=0,014) e verniz fluoretado + laser de Nd:YAG (p=0,025), em comparação aos tratados com verniz não fluoretado. Observou-se que, independentemente da associação aos lasers (Er:YAG ou Nd:YAG), o verniz fluoretado foi capaz de promover a redução da permeabilidade da dentina radicular erodida. Não se observou efeito adicional com a associação dos tratamentos. / The present study aimed to evaluate in situ the effect of associating the fluoride varnish to Er:YAG or Nd:YAG laser at permeability of eroded root dentin. Forty-eight specimens of bovine root dentin (2x2x2mm) were subjected to initial erosive challenge with citric acid (0.3%, pH 3.2), for 2 hours under agitation and stored at artificial saliva, at 37&deg C, for 24 hours, followed by a remineralization period in artificial saliva. After that, specimens were divided according to the treatment: fluoride varnish and non-flouride varnish, and subdivided according to the irradiation: Er:YAG laser (100mJ, 3Hz), Nd:YAG laser (70mJ, 15Hz) and non-irradiated. After a lead-in period (2 days), 8 volunteers (n=8) wore a palatal device containing 3 specimens that was subjected to erosive challenges ex vivo, four times a day with citric acid (0.3%, pH3.2), for 90s, during 5 days. At the first experimental phase, half of volunteers wore devices containing specimens treated with fluoride varnish, fluoride varnish + Er:YAG laser and fluoride varnish + Nd:YAG laser, and the other half wore the specimens treated with non-fluoride varnish, non-fluoride varnish + Er:YAG laser and non-flouride varnish + Nd:YAG laser. After a wash-out period (15 days), volunteers were crossed to different treatment, characterizing a 2x2 cross-over experiment. At the end of each experimental phase, the dentinal permeability was evaluated. Two-way ANOVA and Duncans test revealed a significant difference between specimens treated with fluoride varnish (p=0,005), fluoride varnish + Er:YAG laser (p=0,014) and fluoride varnish + Nd:YAG (p=0,025) compared to specimens treated with no-fluoride varnish. It was observed that regardless of association to laser (Er:YAG or Nd:YAG), fluoride varnish was able to promote, in situ, the reduction of permeability of eroded root dentin, but no additional effect was observed when the treatments were associated.

An investigation in to a novel pivot point free external cavity tunable laser (PPI ECTL). Existing external cavity tunable lasers are constructed using tunable optics, such as Bragg gratings to manipulate the cavity length. These elements although functional provide instability with prolonged use as they are defined by a centre of rotation or pivot point. The aim of this research was to provide a lab demonstrator of a new concept tunable laser based on conventional designs. The novel approach to the system design was in the removal of a defined pivot point, whilst still maintaining a moving optical component. The demonstration system will investigate the improvements upon traditional methods of tuning whilst providing greater tuning range and stability. The main defect of conventional systems was the reliance on the defined pivot point of the movable optics. By changing the position of the pivot point, the cavity length will change and the laser mode will change or hop to a side mode. This was known as a mode hop. The objective of the research was to design and implement a durable ECTL with a large tuning range (>200GHz), mode hop free tuning, fibre coupled, circular output beam and a wavelength in the visible. Design and production of a prototype PPI ECT laser that demonstrate the process of mode hop free tuning without the need of a defined pivot point. The impact of the research may lead in to the integration in to lower cost and more reliable commercial applications.

No description available.

Trois composés de structure Bronze de Tungstène Quadratique ont été étudiés sous forme de couches minces élaborées par ablation laser. Il s'agit de Pb2KNb5O15 (PKN), GdK2Nb5O15 (GKN) et K3Li2Nb5O15 (KLN). Les deux premiers composés correspondent aux compositions extrêmes (x = 0 et x = 1) choisies à partir de la solution solide Pb2(1-x)K(1+x)GdxNb5O15 (PKGN) étudiée au préalable sous forme de céramique au LPMC. Ces composés ont été déposés avec succès sur les trois substrats STO, MgO et GG. La température de dépôt a été établie pour être supérieure ou égale à 700°C, tandis que l'orientation et la qualité cristalline des couches dépendent de la pression partielle d'oxygène, variant de 0,01 à 0,3 mbar. Les propriétés cristallographiques et les relations d'épitaxie ont été analysées au moyen d'un diffractomètre 4-cercles implanté au sein du LPMC. La couche de GKN s'épitaxie (001) sur les deux substrats, MgO et STO, avec des microstructures différentes. La maille GKN est contractée sur les deux substrats et ne présente aucune transition de phase en dessous de 600°C. Elle présente, en dessous de 140°C, une commutation résistive avec une bonne endurance et une rétention moyenne. La couche de PKN est orientée [001] à basse pression et [530] à haute pression, sur le même substrat platiné (STO ou GG) ou sur un substrat MgO non tamponné. La couche de KLN orientée [001] a montré aussi une bonne qualité cristalline sur le substrat MgO. Les couches de GKN et de PKN sont transparentes dans le visible. Celles de GKN et KLN présentent des propriétés ferroélectriques macroscopiques. L'association de GKN et BT en superréseaux n'ont pas permis d'amplifier la réponse ferroélectrique / Three compounds with Tetragonal Tungsten Bronze (TTB) type struc-ture were studied as thin films grown by Pulsed Laser Deposition from pure oxide ceramics. These compounds are Pb2KNb5O15 (PKN), GdK2Nb5O15 (GKN) and K3Li2Nb5O15 (KLN). PKN and GKN correspond to the compositions (x = 0 and x = 1) selected from the solid solution Pb2(1-x)K(1+x)GdxNb5O15 (PKGN), previously studied as ceramics in LPMC. The deposition parameters were optimized to grow oriented thin films. The films were integrated in parallel plate capacitor structures in order to evaluate their electrical properties. GKN film was successfully epitaxially grown on two different substrates, MgO and STO, with different microstructures. GKN unit cell is oriented [001] and is under stress that removed the phase transition and led to resistive switching in GKN films. Promising endurance and retention performances were been demonstrated below 140°C. The obtained films suffer initially from leakage current that was reduced by thermal treatment in oxygen rich atmosphere. Indeed, leakage and resistive switching were found due to oxygen vacancies created during the deposition process. The orientation of PKN thin film was also controlled on Pt coated substrates. [001] ([530]) orientation was achieved using low (high) pressure during the growth process. Crystalline quality of KLN [001] thin film was significantly enhanced using MgO substrate. CV measurements performed on different films, demonstrate the ferroelectric properties in GKN and KLN thin films. However, Coupling GKN and BT in superlattices did not allow enhanced ferroelectric properties. Transparency of GKN and PKN films was demonstrated and their different optical parameters were determined

The aim of this thesis was to discover the mechanism for non-photochemical laser-induced nucleation (NPLIN), which is a technique for inducing nucleation of crystals with laser light without absorption. The mechanism of the optical Kerr effect (OKE) was suggested by Garetz et al. [Physical Review Letters 77, 3475–3476 (1996)] to give an explanation for NPLIN. Since the feasibility of the OKE mechanism for NPLIN has been questioned, a series of experiments on NPLIN of aqueous supersaturated urea were carried out to quantify the relationship between crystal alignment and laser polarization. Digital imaging of crystal growth during laser irradiation showed that nascent needle-shaped crystals of urea were not aligned with the direction of the electric field of the laser. Additionally, work on glycine was aimed at verifying the possibility to control the polymorph of the obtained crystal via the laser polarization. However, our finding shows that the probability of γ-glycine is more likely to increase with increasing supersaturation; and the influence of laser polarization on the resulting morphologies is not strong as reported by Sun et al. [Crystal Growth & Design 6, 684–689 (2006)]. Furthermore, in another work on NPLIN of L-histidine, based on Sun et al. [Crystal Growth & Design 8, 1720–1722 (2008)], we were unable to reproduce the results as stated in Sun’s published paper. We find their results exhibit a large uncertainty when recalculated through the Wilson score interval for binomial distributions. On account of these revised uncertainties, it is unlikely that laser polarization gives polymorphism control. Comparison with the nucleation probability of unfiltered samples in the work of urea and glycine shows that the number of filtered samples nucleated as a result of NPLIN was largely decreased. Moreover, experiments on NPLIN of NaCl and KCl also exhibited that the number of filtered samples nucleated was significantly lower than that of unfiltered samples. This downward tendency in nucleation probability after filtration cannot be explained by Garetz’s OKE mechanism. On account of this, an alternative mechanism named particle-heating mechanism was proposed, and supported by experiments on NPLIN of sodium acetate. Sodium acetate experiments showed that the crystallization of sodium acetate can be induced by a single pulse of a nanosecond laser (1064 nm) with minimum power of 0.1 J cm−2. As discovered by Oliver et al. [D. Oliver, PhD Thesis, Edinburgh University, 2014], anhydrous or trihydrate sodium acetate can be formed under the effects of different organic and inorganic additives, such as poly- (methacrylic acid) and disodium hydrogen phosphate. We demonstrate that crystalline growth velocities and crystal morphology can be influenced by these additives. We find that high levels of additive cause only nucleation of bubbles. By counting the number of crystals, which is approximately consistent to the number of bubbles observed, video microscopy of laser-induced crystallization of sodium acetate has revealed that the general mechanism of NPLIN is most likely to be caused by a particle-heating mechanism. Chapter 8 of the thesis describes a number of solute molecules that were tested using NPLIN, but failed. In terms of improvements for future work or a perspective on NPLIN, detailed suggestions have been described in Chapter 9, which also gives a summary of all work presented.

Anti-resonant hollow core fibre is a new kind of optical fibre waveguide in which light is trapped in a hollow core surrounded by the capillary formed microstructured cladding. This fibre exhibits high damage threshold, low dispersion and ultra-low nonlinearity with relatively low loss of a few tens of dB/km. Its intrinsic feature of multimode delivery limits the applications with high requirements of single mode transmission. In my thesis, I demonstrate how the design of hollow core fibre can be improved with single mode guidance. S2 imaging measurement was used to analyse the mode content of the solid core fibres. In my research, I established S2 measurement to measure the mode contents in hollow core fibres for the first time. Two hollow core fibres with 8 capillaries and 7 capillaries in their claddings were fabricated in same fashion and showed differences in low attenuations. By comparing the mode contents in both of the fibres via S2 imaging measurement, 7-capillary HCF was demonstrated to give better performance on single mode guidance. Among the applications of the HCF, the property of delivering high power in HCF makes the gas filled HCF laser possible. In my research, a continuous-wave mid-infrared acetylene filled hollow core laser was built with a slope efficiency of 33% and an output power of over 1 watt at the wavelength region of 3.1~3.2 μm. The pump source is an Erbium-doped fibre amplified tunable laser diode which works at C-band wavelength. The fibre without the gain medium has two transmission bands with low attenuation of 0.037 dB/m and 0.063 dB/m at pumping and lasing wavelengths respectively. This laser system works in either cavity-based configuration or single pass ASE configuration. The latter configuration shows a better performance in high output power and high slope efficiency. The optimized laser system was studied experimentally with the proper fibre length and gas pressure. This laser system could be extended to be filled with other molecules to longer wavelengths and has potential for high power output.

by Mohammad Siddiq. / Thesis (Ph.D.)--Chinese University of Hong Kong, 1996. / Includes bibliographical references (leaves 167-176). / Abstract --- p.I / Acknowledgment --- p.II / Contents --- p.III / Abbreviations --- p.iv / List of Figures --- p.vi / List of Tables --- p.xiv / Chapter 1 --- Introduction --- p.1 / Chapter 2. --- Theoretical background / Chapter 2.1 --- Static light scattering --- p.5 / Chapter 2.2 --- Dynamic light scattering --- p.17 / Chapter 2.3 --- Chain flexibility --- p.25 / Chapter 3. --- Instrumentations / Chapter 3.1 --- Laser Light Scattering (LLS) measurements --- p.34 / Chapter 3.2 --- Refractive index increment --- p.34 / Chapter 3.3 --- Size Exclusive Chromatography (SEC) --- p.37 / Chapter 4. --- LLS Study of Novel Thermoplastics --- p.38 / Chapter 5. --- LLS Study ofPoly(sulfoalkyl Methacrylate)s --- p.96 / Chapter 6. --- LLS Study of soluble Polyimides --- p.112 / Chapter 7. --- LLS and SEC Study of Hydroxy ethyl Cellulose acetates --- p.135 / Chapter 8. --- LLS Study of hydrolyzed and unhydrolyzed polyacrylamides --- p.153 / Chapter 9. --- References --- p.167 / Chapter 10. --- List of Publications --- p.177

No description available.