Yeung Shun-hin. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 52-54). / Abstracts in English and Chinese. / TITLE PAGE --- p.i / THESIS COMMITTEE --- p.ii / ABSTRACT (ENGLISH) --- p.iii / ABSTRACT (CHINESE) --- p.iv / ACKNOWLEDGEMENTS --- p.v / TABLES OF CONTENTS --- p.vi / LIST OF FIGURES --- p.viii / LIST OF TABLES --- p.x / Chapter Chapter 1 --- Introduction --- p.1 / Chapter Chapter 2 --- Computer-controlled Data Acquisition and Frequency Calibration System for a Ti: sapphire laser spectrometer --- p.3 / Chapter Section 2A --- Motivation and Overview --- p.3 / Chapter Section 2B --- The Hardware --- p.5 / Chapter Section 2C --- The Program --- p.12 / Chapter Section 2D --- Summary --- p.27 / Chapter Chapter 3 --- Cavity Enhanced Absorption Spectroscopy Using Phase-Sensitive Detection --- p.28 / Chapter Section 3A --- Motivation --- p.28 / Chapter Section 3B --- Cavity ring-down technique: the background --- p.29 / Chapter Section 3C --- Cavity enhanced absorption spectroscopy: a historical review --- p.34 / Chapter Section 3D --- Experimental Apparatus --- p.37 / Chapter Section 3E --- Results of Performance tests --- p.41 / Chapter Section 3F --- Applications --- p.45 / Chapter Section 3G --- Summary --- p.49 / Chapter Chapter 4 --- Concluding Remarks --- p.50 / REFERENCES --- p.52

Thesis. 1977. Sc.D.--Massachusetts Institute of Technology. Dept. of Physics. / Microfiche copy available in Archives and Science. / Bibliography : leaves 221-223. / by Riad Ahmad Bitar. / Sc.D.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1979. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Includes bibliographical references. / Ph.D.

Centros de cor e íons de metal de transição em cristais iônicos tem mostrado um grande potencial como candidatos a meios laser ativos sintonizáveis. Para determinar se tais materiais são apropriados ou não para operar como meios laser, seus parâmetros espectroscópicos fundamentais tem de ser conhecidos. No presente trabalho, nos descrevemos um metodo espectroscópico que permite determinar o diagrama de níveis de energia da espécie investigada, o tempo de decaimento, a eficiência quântica e a secção de choque de emissão. O tempo de decaimento foi medido usando-se um bombeamento senoidal de excitação e detecção sensível a fase; obtendo-se 1,6ms para o kcl:TL POT.0 (1), 17ns para o LIf:F IND.2, 28ns para o LIf:F2 POT.+ E 4ns para o LIf:F3 POT.+. Usando-se uma técnica de absorção rotulada foi possível determinar absorções do estado fundamental e do primeiro estado excitado da espécie investigada mesmo com a interferência de outros centros. Técnica utilizada em kcl:tl onde níveis de energia do centro de cor de TL POT.0 (1) foram identificados vários outros agregados de tl devido a preparação do cristal, que perturbam o centro TL POT.0 (1) também foram identificados. Vários outros agregados de T1, devido a preparação do cristal, que perturbam o centro TL POT.0 (1), também foram observados. / Color centers and transition metal ions in ionic crystals have shown a qreat potential as candidates for tunable laser sources. In order to determine whether or not such materials are suitable to operate as laser media, their fundamental spectroscopic parameters have to be known. In the present work we describe a spectroscopic method that can determine the energy level diagram of the species under investigation, the decay time, quantum efficiency and emission cross section. Firstly, the decay time was measured by using a sinosoidal pumping excitation and phase sensitive detection. Using a specially home designed cryostat we were able to measure the decay time in the temperature range of 77K to 310K, and therefore, the temperature dependence of the quantum efficiency. This technique was applied to the T1°(1):KCl, F2:LiF, F+3:LiF and F+2:LiF, where decay times of 1.6s, 17ns, 4ns and 28ns were measure, respectively. Secondly, by using a pump-probe technique we were able to determine the excited-state absorption of the studied species, even under the interference of other centers. This is particularly important in color centers due to the presence of several other species during the centers formation. Besides, this technique can identify excited state absorptions that can eliminate laser medium candidates. This technique was used in KCl:T1 crystals where laser active Tl° (1) color center energy levels were identified. Besides, several other Tl aggregates due to the crystal preparation that perturb the Tl° (1) center were also observed.

Abstract not available

We present a detailed experimental investigation into Bose-Einstein condensates loaded into a one-dimensional optical standing wave at the Bragg condition. The main emphasis of this thesis is the experimental and theoretical investigation into Bragg spectroscopy performed on circularly accelerating Bose-Einstein condensates. The condensate undergoes circular micromotion in a magnetic time-averaged orbiting potential trap and the effect of this motion on the Bragg spectrum is analysed. A simple frequency modulation model is used to interpret the observed complex structure, and broadening effects are considered using numerical solutions to the Gross-Pitaevskii equation. The second part of this thesis is an experimental investigation into the effect of nonlinearity on the non-adiabatic loading of a condensate into a optical lattice at the Brillouin zone boundary. Results of using a phase shifting technique to load a single Bloch band in the presence of strong interactions are presented. We observe a depletion of the condensed component, and we propose possible mechanisms for this result.

Thesis (Ph. D.)--University of Chicago, Department of Chemistry and Department of Astronomy and Astrophysics, June 2001. / Includes bibliographical references. Also available on the Internet.

An all-solid-state continuous-wave (cw) laser system for mid-infrared absorption measurements of the carbon monoxide (CO) molecule has been developed and demonstrated. The single-mode, tunable output of an external-cavity diode laser (ECDL) is difference-frequency mixed (DFM) with the output of a 550-mW diode-pumped cw Nd:YAG laser in a periodically-poled lithium niobate (PPLN) crystal to produce tunable cw radiation in the mid-infrared. The wavelength of the 860-nm ECDL can be coarse tuned between 860.78 to 872.82 nm allowing the sensor to be operated in the 4.4 – 4.8 µm region. Results from single-pass mid-IR direct absorption experiments for CO concentration measurements are discussed. CO measurements were performed in CO/CO2/N2 mixtures in a room temperature gas cell that allowed the evaluation of the sensor operation and data reduction procedures. Field testing was performed at two locations: in the exhaust of a well-stirred reactor (WSR) at Wright-Patterson Air Force Base and the exhaust of a gas turbine at Honeywell Engines and Systems. Field tests demonstrated the feasibility of the sensor for operation in harsh combustion environments but much improvement in the sensor design and operation was required. Experiments in near-adiabatic hydrogen/air CO2-doped flames were performed featuring two-line thermometry in the 4.8 µm spectral region. The sensor concentration measurement uncertainty was estimated at 2% for gas cell testing. CO concentration measurements agreed within 15% of conventional extractive sampling at WSR, and for the flame experiments the repeatability of the peak absorption gives a system uncertainty of 10%. The noise equivalent CO detection limit for these experiments was estimated at 2 ppm per meter, for combustion gas at 1000 K assuming a SNR ratio of 1.

Microresonators are devices that confine light in small volumes through total internal reflection. Introducing an emissive species into a microresonator allows for resonance enhanced emission at frequencies where the spectrum of the emissive species overlaps with the resonant frequencies of the microresonator. Previous research has led to a good understanding of these phenomena in 1D and 2D microresonators, but many 3D microresonator geometries have not yet been investigated. This work details the successful creation and demonstration of a cubic polymeric optical microresonator.

<p>Atmospheric corrosion, the most common form of metal corrosion, occurs within the interfacial region between a solid, and the surrounding atmosphere. In fact three phases and two interfaces are involved: the gas, a thin liquid layer, a solid, the gas/liquid and the liquid/solid interfaces. In this thesis, the vapor/liquid and liquid/metal interfaces have been studied by the in-situ techniques vibrational sum frequency spectroscopy (VSFS), and infrared reflection/absorption spectroscopy (IRAS). The main focus has been on characterization of the corrosive organic molecules formic acid, acetic acid, and acetaldehyde, at the two interfaces. Additionally, the headgroup of sodium dodecyl sulfate (SDS) has been examined at the air/water interface.</p><p>VSFS is an inherently surface sensitive laser spectroscopy technique, which provides vibrational spectra solely of the molecules residing at the surface of for example a liquid, despite the vast excess of the same molecules in the bulk. To obtain a comprehensive molecular picture of the organic compounds at the air/liquid interface, studies have been undertaken in several spectral regions, targeting the CH, C=O, C-O, OH, and SO3 stretching vibrations. Furthermore, the surrounding water molecules have been investigated in order to study hydration phenomena. Acetaldehyde has been determined to partly form a gem-diol (CH3CH(OH)2) at the air/water interface, whereas acetic acid forms various hydrogen-bonded species, with hydrated monomers at low concentrations and centrosymmetric cyclic dimers at high concentrations. Formic acid was found to form a different complex at very high concentrations, in addition to the species observed at low concentrations. Performing experiments with different polarizations of the laser beams has enabled the determination of the orientation of the interfacial molecules. The methyl group of acetic acid was concluded to be oriented close to the surface normal throughout the concentration range, whereas the tilt angle of the CH group of formic acid was determined to be ~35°. The SDS studies revealed that the headgroup orientation is constant in a wide range of concentrations, and also in the presence of sodium chloride.</p><p>IRAS has provided information regarding the composition and kinetics of the corrosion products formed upon exposure of a zinc oxide surface to the organic compounds. The importance of the water adlayer on metal surfaces has been confirmed by the faster kinetics observed at higher relative humidities. Exposure to formic acid resulted in the formation of zinc formate, whereas both acetic acid and acetaldehyde formed zinc acetate upon reaction with the zinc oxide surface. However, the kinetics were faster for acetic acid than acetaldehyde, which was explained in terms of an acetate-induced zinc dissolution process and a more complicated reaction path involved in the acetaldehyde case to form the zinc acetate surface species. Scanning electron microscopy indicated the formation of radially growing reaction products for acetic acid and filiform corrosion for acetaldehyde.</p>