This thesis aims to investigate the possibility of developing spectroscopic techniques for trace gas detection, with particular emphasis on their applicability to breath analysis and medical diagnostics. Whilst key breath molecules such as methane and carbon dioxide will feature throughout this work, the focus of the research is on the detection of breath acetone, a molecule strongly linked with the diabetic condition. Preliminary studies into the suitability of cavity enhanced absorption spectroscopy (CEAS) for the analysis of breath are carried out on methane, a molecule found in varying quantities in breath depending on whether the subject is a methane-producer or not. A telecommunications near-infrared semiconductor diode laser (1.6 µm) is used with an optical cavity based detection system to probe transitions within the vibrational overtone of methane. Achieving a minimum detectable sensitivity of 600 ppb, the device is used to analyse the breath of 48 volunteers, identifying approximately one in three as methane producers. Following this, a second type of laser source, the novel and widely tunable Digital Supermode Distributed Bragg Reflector (DS-DBR) laser, is characterised and the first demonstration of its use in spectroscopy documented. Particular emphasis is given to its application to CEAS and to probing the transitions of the two Fermi resonance components of the CO_2 3ν_1 + ν_3 combination bands found within the spectral range (1.56 - 1.61 µm) of the laser, providing the means to determine accurate ^{13}CO_2/^{12}CO_2 ratios for use in the urea breath test. Not all molecules exhibit narrow, well-resolved ro-vibrational transitions and the next section of the thesis focuses on the detection of molecules, such as acetone, with broad, congested absorption features which are not readily discernible using narrowband laser sources. To provide the necessary specificity for these molecules, two types of broadband source, a Superluminescent Light Emitting Diode (SLED) and a Supercontinuum source (SC), both emitting over the 1.6 - 1.7 µm region, are used in the development of a series of broadband cavity enhanced absorption (BB-CEAS) spectrometers. The three broadband absorbers investigated here, butadiene, acetone and isoprene, all exhibit overtone and combination bands in this spectral region and direct absorption measurements are taken to determine absorption cross-sections for all three molecules. The first BB-CEAS spectrometer couples the SLED device with a dispersive monochromator, attaining a minimum detectable sensitivity of 6 x 10^{-8} cm^{-1}, which is further enhanced to 1.5 x 10^{-8} cm^{-1} on replacing the monochromator with a Fourier Transform interferometer. The spectral coverage is then extended to 1.5 - 1.7 µm by coupling the first SLED with a second device, providing a demonstration of simultaneous multiple species detection. Finally, a SC source is used to provide greater power and uniform spectral intensity, resulting in an improved minimum detectable sensitivity of 5 x 10^{-9} cm^{-1}, or 200 ppb, 400 ppb and 200 ppb for butadiene, acetone and isoprene respectively. This device is then applied to acetone-enriched breath samples; the resulting spectra are fitted with a simulation to return the acetone levels present in the breath-matrix. Following this, the development of a prototype breath acetone analyser, carried out at Oxford Medical Diagnostics Ltd. (OMD), is described. To fulfill the requirements of a compact and commercially-viable device, a diode laser-based system is used, which necessitates a thorough investigation into all possible sources of absorption level change. Most notably, this includes a study into the removal and negating of interfering species, such as water vapour, and to a lesser extent, methane. A novel solution is presented, utilising a water-removal device in conjunction with molecular sieve so that each breath sample generates its own background, which has allowed breath acetone levels to be measured within an uncertainty of 200 ppb. Spectroscopic detection then moves to the mid-infrared with the demonstration of a continuous wave 8 µm quantum cascade laser, which allows the larger absorption cross-sections associated with fundamental vibrational modes to be probed. Following the laser's characterisation using methane, including a wavelength modulation spectroscopy study, the low effective laser linewidth is utilised to resolve rotational structure in low pressure samples of pure acetone. Absorption cross-sections are determined before the sensitivity of the system is enhanced for the detection of dilute concentrations of acetone using two types of multipass cells, firstly a White cell and secondly a home-built Herriott cell. This allows an acetone minimum detectable absorption of 350 ppb and 20 ppb to be attained, respectively. Following this, an optical cavity is constructed and, on treating breath samples in a water-removal device prior to analysis, breath acetone levels determined and corroborated with a mass spectrometer. Finally, a preliminary study probing acetone in the ultraviolet is presented. Utilising an LED centred at 280 nm with a low finesse optical cavity and an imaging spectrograph, detection of 25 ppm of acetone is demonstrated and possible vibronic structure resolved. Combining large absorption cross-sections with the potential to be compact and commercially viable, further development of this arrangement could ultimately represent the optimum solution for breath acetone detection.

Imaging mass spectrometry (IMS) in microscope mode allows the spatially resolved molecular constitution of a large sample section to be analysed in a single experiment. If performed in a linear mass spectrometer, the applicability of microscope IMS is limited by a number of factors: the low mass resolving power of the employed ion optics; the time resolution afforded by the scintillator screen based particle detector and the multi-hit capability, per pixel, of the employed imaging sensor. To overcome these limitations, this thesis concerns the construction of an advanced ion optic employing a pulsed extraction method to gain a higher ToF resolution, the development of a bright scintillator screen with short emission lifetime, and the application of the Pixel Imaging Mass Spectrometry (PImMS) sensor with multi-mass imaging and time stamping capabilities. Initial experimental results employing a three electrode ion optic to spatially map ions emitted from a sample surface are presented. By applying a static electric potential a time-of-flight resolution of t/2Δt=54 and a spatial resolution of 20 μm are determined across a field-of-view of 4 mm diameter. While the moderate time-of-flight resolution only allows particles separated by a few Dalton to be distinguished, the instrument is used to demonstrate the multi-mass imaging capabilities of the PImMS sensor when being applied to image grid structures or tissue samples. An improved time-of-flight resolution is achieved by post extraction differential acceleration of a selected range of ions (up to 100 Da) using a newly developed five electrode ion optic. This modification is shown to correct the initial velocity spread of the ions coming off the sample surface, which yields an enhanced time-of-flight resolution of t/2Δt=2000 . The spatial resolution of the instrument is found to be 20 μm across a field-of-view of 4 mm. Adjusting the extraction field strength applied to the ion optic of the constructed mass spectrometer allows the optimised mass range to be tuned to any mass of interest. Ion images are recorded for various samples with comparable spatial and ToF resolution. Hence, studies on tissue sections and multi sample arrays become accessible with the improved design and operational principle of the microscope mode IMS instrument. A fast and efficient conversion of impinging ions into detectable flashes of light, which can consequently be recorded by a fast imaging sensor, is essential to maintain the achievable time-of-flight and spatial resolution of the IMS instrument constructed. In order to find a suitable fast and bright scintillator to be applied in a microchannel based particle detector, various inorganic and organic substances are characterised in terms of their emission properties following electron excitation. Poly-para-phenylene laser dye screens are found to show an outstanding performance among all substances analysed. An emission life time of below 4 ns and a brightness exceeding that of a P47 screen (industry standard) by a factor 2× is determined. No signal degradation is observed over an extended period, and the spatial resolution is found to be comparable to commercial imaging detectors. Hence, these scintillator screens are fully compatible with any ion imaging application requiring a high time resolution. In a further series of mass spectrometric experiments, ions are accelerated onto a scintillator mounted in front of a multi pixel photon counter. The charged particle impact stimulated the emission of a few photons, which are collected by the fast photon counter. Poly-para-phenylene laser dyes again show an outstanding efficiency for the conversion of ions into photons, resulting in a signal enhancement of up to 5× in comparison to previous experiments, which employed an inorganic LYSO scintillator.

Thin film multiferroic oxides with co-existing ferroelectric and ferromagnetic ordering have attracted much interest in recent years, partly as a result of the enhancements achieved through the adoption of strained thin film geometries. This thesis presents work on two such thin film oxides; lanthanide substituted BiFeO₃ and Fe substituted PbTiO₃. Coherent magnons and acoustic phonons were impulsively excited and probed in thin films of the room temperature multiferroic Bi_1-x-yDy_xLa_yFeO₃ using femtosecond laser pulses. The elastic moduli of rhombohedral, tetragonal and rare-earth doped BiFeO₃ were determined from acoustic mode frequencies in conjunction with spectroscopic ellipsometry. A weak ferromagnetic order, induced alternately by magnetization in the growth direction or by tetragonality, created a magnon oscillation at 75 GHz, indicative of a Dzyaloshinskii-Moriya interaction energy of 0.31 meV. Bulk crystals and thin films of PbTi_1-xFe_xO₃ (PTFO) are multiferroic, exhibiting ferroelectricity and ferromagnetism at room temperature. Here we report that the Ruddlesden-Popper phase Pb_n+1(Ti_1-xFe_x)_nO_3n+1 forms spontaneously during pulsed laser deposition of PTFO on LaAlO₃ substrates. High-resolution transmission electron microscopy, x-ray difraction and x-ray photoemission spectroscopy were utilised to perform a structural and ompositional analysis, demonstrating that n≃8 and x≃0.33. The complex dielectric function of the films was determined from far-infrared to ultraviolet energies using a combination of terahertz time-domain spectroscopy, Fourier transform spectroscopy, and spectroscopic ellipsometry. The simultaneous Raman and infrared activity of phonon modes, and the observation of second harmonic generation, establishes a non-centrosymmetric point group for Pb_n+1(Ti_0.67Fe_0.33)_nO_3n+1-δ consistent with ferroelectricity. No evidence of macroscopic ferromagnetism was found in SQUID magnetometry. The ultrafast optical response exhibited coherent magnon oscillations compatible with local magnetic order, and additionally was used to study photocarrier cooling on picosecond timescales. An optical gap smaller than that of BiFeO₃ and long photocarrier lifetimes may make this system interesting as a ferroelectric photovoltaic.

This work is devoted to the investigation of a spin polarization in ferromagnetic semiconductor Ga1-xMnxAs with a broad nominal concentration of manganese ions using one method of the ultrafast laser spectroscopy - the time-resolved Kerr rotation. At first, the experimental setup was optimized for the investigation of the dynamics of spin polarized charge carriers in semiconductors which were photo-generated by circularly polarized laser pulses. It was observed that the measured signal is induced by spin-polarized electrons. Due to a small thickness of the investigated ferromagnetic films the measured signal probably monitored the dynamics of fotogenerated electrons in GaAs substrate. Nevertheless, the measured data show that the electron spin dynamics in the substrate is significantly influenced by proximity effect due to the deposited ferromagnetic layer.

INTRODUCTION: The“vulnerable plaque" is defined as the“precursor lesion" that ultimately ends in acute coronary thrombi (clots) that create a heart attack. Macrophages and inflammatory cells, found preferentially in vulnerable plaque, sustain their activity in the plaque through anaerobic metabolism and lactate production. The ultimate goal is to assess anaerobic metabolism in-vivo by measuring tissue pH and lactate concentration in atherosclerotic plaques using optical spectroscopy. The proposed in-vitro optical probe design, experimental method, and spectroscopic data analysis methodology are established in this research. METHODS: A fiber optic probe was designed and built based on both Monte Carlo simulations and bench testing with the goal to collect light from a small volume of tissue. A simulation of the depth penetration of the proposed probe was performed on normal and atherosclerotic aortic tissue, and the final probe was bench tested using normal aorta. A method was developed to preserve plaque metabolic status of tissue harvested from patients. Human atherosclerotic tissue obtained immediately after carotid endarterectomy was placed in Minimum Essential Medium (MEM) with non-essential amino acids supplement, bubbled with 75%O2/20%N2/5%CO2 at 37°C. Tissue pH, pCO2, pO2 and temperature with (n=7) and without (n=2) the media preparation over time were reviewed to assess plaque viability and maintenance of physiological conditions. Additional plaques placed in media were used for development of chemometric methods to measure pH and lactate. Areas of each plaque were randomly chosen for analysis. Reflectance spectra were collected with a dispersive spectrometer (400-1100 nm) and a Fourier-transform near-infrared spectrometer (1100-2400 nm) using the fiber optic probe. Reference measurements for tissue pH and lactate were made with glass microelectrodes and micro-enzymatic assay, respectively. Partial least-squares (PLS) data analysis was used to develop multivariate calibration models on an initial set of 5-6 plaques relating the optical spectra to the reference tissue pH (n=20) or the lactate concentration (n=21) to assess data quality. The coefficient of multiple determination (R2), the standard error of cross-validation (SECV), and the number of factors were used to assess the model performance. Additional points were collected from ~14 plaques and added to preliminary data. Pre-processing techniques were then used to see if preliminary data results could be improved by reducing different sources of variability with the introduction of more points. RESULTS: Monte Carlo simulations and depth penetration tests with the final probe design showed light is collected from ~1 mm3 volume of tissue using a 50 micron source-receiver separation. Tissue pH, pCO2, pO2 and temperature values demonstrated that the plaques were viable and stable in the media preparation for a maximum of 4 hours. Data from the first six plaques collected for lactate analysis showed that for seventeen points, a six-factor model produced adequate results (R2=0.83 SECV=1.4 micromoles lactate/gram tissue). Data from the first five plaques collected for tissue pH analysis, showed for seventeen different points, a three-factor model produced adequate results (R2=0.75 SECV=0.09 pH units). When additional points were added to either data set, model results were degraded. CONCLUSIONS: The in-vitro optical probe design and experimental procedures was established and the feasibility of the optical method demonstrated with preliminary data. However, with the addition of more data points, different sources of tissue and spectral variability were observed to affect calibration. The gross pathology type and mismatched optical volume to reference measurement volume limited the tissue pH determination. The reference measurement precision, the spatial resolution of the reference lactate measurement, and unmodeled tissue variability (water and proteins) limited the lactate determination. Large variability in all optical measurements was observed. Additional in-vitro data collection would be required such that the variability due to the tissue is reduced and any spectrometer variability adequately compensated to be able to use the optical calibration in-vivo.

Thesis (Ph.D.)--Massachusetts Institute of Technology, Dept. of Physics, 1980. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND SCIENCE. / Vita. / Bibliography: leaves 140-145. / by Walter Peter Lapatovich. / Ph.D.

This work centres around development and applications of the Resonance Ionization Laser Ion Source (RILIS) of the ISOLDE radioactive ion beam facility based at CERN. The RILIS applies step-wise resonance photo-ionization, to achieve an unparalleled degree of element selectivity, without compromising on ion source efficiency. Because of this, it has become the most commonly used ion source at ISOLDE, operating for up to 75% of ISOLDE experiments. In addition to its normal application as an ion source, the RILIS can be exploited as a spectroscopic tool for the study of nuclear ground state and isomer properties, by resolving the influence of nuclear parameters on the atomic energy levels of the ionization scheme. There are two avenues of development by which to widen the applicability of the RILIS: laser ionization scheme development, enabling new or more efficient laser ionized ion beams and the development of new laser-atom interaction regions. New ionization schemes for chromium, tellurium, germanium, mercury and radium have been determined. Additionally, for the first time, the anode cavity of the VADIS, ISOLDE's variant of the FEBIAD type arc discharge ion source was used as the laser-atom interaction region. A new element selective RILIS mode of operation was established, enabling the ISOLDE RILIS to be coupled with molten targets for the first time, increasing the flexibility of ISOLDE operation and opening a direction for future developments. This combined ion source was termed the VADLIS or Versatile Arc Discharge and Laser Ion Source. A combination of the developments presented in this thesis: an improvement of the laser ionization efficiency and the ability to couple the RILIS with molten targets, satisfied the pre-requisites for the long-awaited extension of the laser spectroscopy studies of exotic mercury isotopes. A sudden onset of extreme shape staggering in the neutron deficient mercury isotopes was revealed by optical pumping and laser spectroscopy experiments at ISOLDE in the 1970s and 1980s, with measurements conducted down to 181Hg. Despite this being one of the most remarkable examples of shape coexistence in the nuclear chart, in the intervening decades the cessation point of this odd-even staggering had yet to be unambiguously determined through measurements of nuclear ground state charge radii. This open question was successfully resolved using the ISOLDE RILIS for in-source resonance ionization spectroscopy. The experiment was performed as part of a large collaboration, using the Leuven Windmill system for alpha-detection; direct ion counting with the ISOLTRAP multi-reflection time-of-fight mass spectrometer (MR-ToF MS); and ion beam current measurements using the ISOLDE Faraday cups. The sensitivity of the technique enabled the measurements to be extended down to 177Hg, providing a definitive answer, that the extreme shape staggering stops at 180Hg. In addition to extending the measurements at the neutron deficient end of the mercury isotope chain, the relative mean square charge radii of both 207Hg and 208Hg was determined. This extended the measurements beyond the N = 126 shell closure, enabling the characterization of the "kink" in the trend of the isotope shifts.

Cavity ringdown spectroscopy (CRDS) makes use of light retention in an optical cavity to enhance the sensitivity to absorption or extinction of light from a sample inside the cavity. When light entering the cavity is stopped, the output is an exponential decay with a decay constant that can be used to determine the quantity of the analyte if the extinction or absorption coefficient is known. The precision of the CRDS is dependent on the rate at which the system it acquires and processes ringdowns, assuming randomly distributed errors. We have demonstrated a CRDS system with a ringdown acquisition rate of 1.5 kHz, extendable to a maximum of 3.5 kHz, using new techniques that significantly changed the way in which the ringdowns are both initiated and processed. On the initiation side, we combined a custom high-resolution laser controller with a linear optical feedback configuration and a novel optical technique for initiating a ringdown. Our optical injection "unlock" method switches the laser off-resonance, while allowing the laser to immediately return to resonance, after terminating the unlock, to allow for another ringdown (on the same cavity resonance mode). This part of the system had a demonstrated ringdown initiation rate of 3.5 kHz. To take advantage of this rate, we developed an optimized cost-effective FGPA-based data acquisition and processing system for CRDS, capable of determining decay constants at a maximum rate of 4.4 kHz, by modifying a commercial ADC-FPGA evaluation board and programming it to apply a discrete Fourier transform-based algorithm for determining decay constants. The entire system shows promise with a demonstrated ability to determine gas concentrations for H2O with a measured concentration accuracy of ±3.3%. The system achieved an absorption coefficient precision of 0.1% (95% confidence interval). It also exhibited a linear response for varying H2O concentrations, a 2.2% variation (1σ) for repeated measurements at the same H2O concentration, and a corresponding precision of 0.6% (standard error of the mean). The absorption coefficient limit of detection was determined to be 1.6 x 10-8 cm-1 (root mean square of the baseline residual). Proposed modifications to our prototype system offer the promise of more substantial gains in both precision and limit of detection. The system components developed here for faster ringdown acquisition and processing have broader applications for CRDS in atmospheric science and other fields that need fast response systems operating at high-precision.

This thesis demonstrates a measurement of a plasma fluctuation velocity-space cross-correlation matrix using laser induced fluorescence. The plasma fluctuation eigenmode structure on the ion velocity distribution function can be empirically determined through singular value decomposition from this measurement. This decomposition also gives the relative strengths of the modes as a function of frequency. Symmetry properties of the matrix quantify systematic error. The relation between the eigenmodes and plasma kinetic fluctuation modes is explored. A generalized wave admittance is calculated for these eigenmodes. Since the measurement is a localized technique, it may be applied to plasmas in which a single point measurement is possible, multipoint measurements may be difficult, and a velocity sensitive measurement technique is available.

An J=1→J=1 atomic system in Samarium with incident laser resonant radiation has been investigated. A linearly polarized laser at 686nm excites atoms from the level 4ƒ[superscript]66s[superscript]2 [superscript]7F[subscript]1 to a excited level 4ƒ[superscript]66s6p [superscript]9F[subscript]1 via the process of optical pumping. When an external magnetic field is applied to the atom-laser interaction and the decay fluorescence collected, a level-crossing profile appears. Theoretical predictions of the level-crossing profile can be made using spherically irreducible tensors to describe the density matrix which take advantage of the symmetry of the atomic system. By comparing theory with experimental data, a discussion is made of the various parameters and external factors that can affect this system, which show that Doppler broadening is the major influence. An additional investigation is made into the evolution of the J=1→J=1 atomic system with increasing laser exposure. Comparisons of the experimental data with theoretical predictions are made by analyzing the FWHM of the overall level-crossing profile, the FWHM of the dip about B = 0 and the relative depth of the dip. By charting the progress of these parameters with increasing laser exposure, it can be seen that the theory and experimental data agree qualitatively. / http://proxy.library.adelaide.edu.au/login?url= http://library.adelaide.edu.au/cgi-bin/Pwebrecon.cgi?BBID=1320338 / Thesis (Ph.D.) -- University of Adelaide, School of Chemistry and Physics, 2008