Laser Induced Breakdown Spectroscopy LIBS is a fast non-contact technique for the analysis of the elemental composition using spectral information of the emission from a laser-induced plasma. For the LIBS studies in this thesis the focus has been in using very low energy, microjoule pulses in order to give high spatial resolution and minimize the laser system requirements. This is a regime that we refer to as microLIBS. Under such conditions it is important to maximize the signal detected to give the lowest limit of detection LOD possible. One technique to improve the signal to noise ratios is by coupling LIBS with Laser Induced Fluorescence. This is a technique where the _rst pulse creates a vapor plume and the second pulse tuned to a resonant absorption line of the species of interest re-excites the plume. We term this technique as Laser ablation Laser Induced Fluorescence LA-LIF. We have been investigating the performance of LA-LIF at low pulse energies (_ 1 mJ for both pulses) for the detection of elemental contaminants in water. This technique allows reasonable performance compared to high energy singlepulse LIBS, but at a much reduced total energy expenditure. This allows LODs in the parts per billion range ppb range which typically cannot be obtained with low energy single pulse probing of the systems. This approach or exceeds the sensitivities which can be obtained with many shots using much larger energy systems. In this thesis we investigated the performance of LIBS at low pulse energies for the detection of Pb as a contaminant in water. An LOD of 70 ppb was obtained for an accumulation of 100 shots with the ablation laser pulse energy of 250 _J and an excitation laser pulse energy of 8 _J. A systematic study of the detector conditions was made for the system for the detection of Pb. Scaling laws for the LOD in terms of the pump and probe energies were measured and also the e_ect of detector gain, the gate delay and the gate width were studied. In this thesis LIBS and LA-LIF were also used to analyze ultralow volumes of analyte in liquids in microuidic geometries. LIBS was applied for the detection of Na in liquid droplets in a microuidic system. The detection of Na as low as 360 femtograms was demonstrated for 100 shots integrated in this system. An LOD of 7 ppm for Pb for 100 shot accumulation was demonstrated using the LA-LIF technique on an 18 _m diameter microdroplet. To study the laser interaction with the water targets the MEDUSA one dimensional hydrocode was used. The propagation of the shockwave and plume dynamics were studied using this modeling code. The expansion of the plume was studied and compared to experimentally measured values and to physical models for blast wave expansion and stagnation. Two preconcentration techniques were also studied, one of which used a wood-chip as a substrate to absorb the analyte liquid and wick the salt on to the surface for analysis and the other used an electroplating technique to plate the analyte metal as a thin _lm on a substrate metal used as a cathode. The electroplating method for preconcentration was also studied using a microchip laser and a LOD of 6.4 ppb for Pb in water was obtained for an accumalation of 200,000 shots. / Photonics and Plasmas

In this thesis, two different experimental approaches to capacitive deionization (CDI) process are presented. In the first approach, transient system characteristics were analyzed to find three different operating points, first based on minimum outlet concentration, second based on maximum average adsorption rate and third based on maximum adsorption efficiency. These three operating points were compared in long term desalination tests. In addition, the effects of inlet stream salinity and CDI system size have been characterized to assess the feasibility of a commercial CDI system operating at brackish water salinity levels. In the second approach, the physical phenomena occurring inside a capacitive deionization system were studied by laser-induced fluorescence visualization of a “pseudo-porous” CDI microstructure. A model CDI cell was fabricated on a silicon-on-insulator (SOI) substrate and charged fluorophores were used to visualize the simultaneous electro migration of oppositely charged ions and to obtain in situ concentration measurements. / text

A new diagnostic technique for studying the turbulent mixing characteristics of supersonic mixing flowfields is developed and implemented in two Mach 3 mixing flowfields. The diagnostic utilizes simultaneous particle image velocimetry and quantitative planar laser-induced fluorescence of krypton gas to study the interaction between turbulent scalar and velocity fields. The fluorescence properties of krypton gas are determined; measurements of the pressure and temperature dependence of the collisional quenching rates and cross-sections are made for various mixtures with krypton. The gases tested in this fashion include helium, nitrogen, air, oxygen, and ethylene. Additional measurements are performed to measure the relative two-photon absorption cross-section for krypton gas. The non-dimensional quenching rates are found to follow a power-law dependence for temperature, while the pressure dependence of the total quenching rate is found to be linear. Two injection flowfields are studied for their general topology and kinematic characteristcs. The first injector model is a basic injector meant to serve as a baseline case; there are no hypermixing elements present in this model. The second model is an asymmetric, unswept hypermixing injector featuring 15 degree expansive ramps flanking a central block. These studies utilize particle image velocimetry in planar and stereoscopic configurations in various planes. Results for the mean flowfield show distinct differences between the two flowfields; the planar injector flowfield is shown to be highly two-dimensional and exhibits minimal coherent unsteady behavior. The hypermixing injector flowfield exhibits a highly three-dimensional wake, with a pair of stream-wise vortices driving both mean deviations in the flowfield and considerable vortical coupling in the span-wise direction. Simultaneous krypton PLIF and PIV are employed in the two mixing flowfields. An assay of the dependence of the krypton mole fraction calculations on the fluorescence signal is performed. The overall sensitivity and the resulting dynamic range of the calibration is dictated largely by the reference mole fraction. Additionally, several different theoretical models of the temperature dependence of the fluorescence signal are studied to assess their validity and influence over the PLIF calibration procedure. Finally, the technique is employed in the two mixing flowfields, and a brief analysis of the mean and unsteady behavior of the two is conducted. / text

No description available.

Studying the intrinsic properties of molecules in the gas-phase is advantageous, since it reduces the complexity present in solution that arises from interactions between the molecule of interest and other species present in the local environment, including those with the solvent itself. In this report, the photophysical properties of gaseous cationic rhodamine B (RBH+) were determined and photodissociation reaction kinetics and power dependence of three prototropic forms of fluorescein; the cation ([F + H]+), monoanion ([F - H]-), and dianion ([F – 2H]-2), each of which possesses their own distinct spectral properties, were measured. The analyte ions of interest were formed via electrospray ionization, mass-selected and stored in a quadrupole ion trap mass spectrometer which has been customized to enable gas-phase spectroscopic studies. Knowledge of the intrinsic photophysical properties of such chromophores in the gas-phase will enable a better understanding of how the local environment of the molecule alters its properties.

Studying the intrinsic properties of molecules in the gas-phase is advantageous, since it reduces the complexity present in solution that arises from interactions between the molecule of interest and other species present in the local environment, including those with the solvent itself. In this report, the photophysical properties of gaseous cationic rhodamine B (RBH+) were determined and photodissociation reaction kinetics and power dependence of three prototropic forms of fluorescein; the cation ([F + H]+), monoanion ([F - H]-), and dianion ([F – 2H]-2), each of which possesses their own distinct spectral properties, were measured. The analyte ions of interest were formed via electrospray ionization, mass-selected and stored in a quadrupole ion trap mass spectrometer which has been customized to enable gas-phase spectroscopic studies. Knowledge of the intrinsic photophysical properties of such chromophores in the gas-phase will enable a better understanding of how the local environment of the molecule alters its properties.

Master of Science / Department of Mechanical and Nuclear Engineering / Steven Eckels / In this thesis, a two-color ratiometric planar laser-induced fluorescence (PLIF) technique for the measurement of temperature fields in liquids is described. The method uses the temperature sensitive rhodamine B and temperature insensitive rhodamine 110 fluorescent dyes. The ratio of the fluorescent emission intensity of these two dyes is inversely proportional to temperature and is independent of laser intensity variation in the flow field. Because the emission spectra of these two dyes overlap, a correction was developed to disentangle the two signals. In addition, the absorption spectra of rhodamine B and rhodamine 110 and emission spectrum of rhodamine 110 overlap, leading to the self-attenuation of the rhodamine 110 signal by the dye solution. A correction with respect to path length was developed for self-attenuation. This thesis presents the calibration process for a PLIF thermometry system and visualization of temperature gradients in a glass water tank with motion induced by large temperature gradients. A step-by-step procedure of the final calibration process is also presented.

La thèse consiste à développer une technique d'imagerie quantitative de concentration de polluants dans les écoulements réactifs. Il s'agit d'une part de développer l'imagerie de fluorescence sur NO. Un modèle de fluorescence à n niveaux a été développé pour calculer l'évolution de la fluorescence avec la température, concentration des espèces et pression. Ce modèle a été validé avec des mesures de fluorescence et d'absorption obtenues dans une cellule optique fonctionnant jusqu'à 800 K et 20 bar puis dans un brûleur laminaire haute-pression. De ce modèle a été définie une stratégie permettant la mesure de la distribution instantanée de NO dans une flamme stratifiée. Une étude similaire pour détecter CO a été ensuite initiée. Des mesures de fluorescence à deux photons ont été obtenues dans la cellule et dans une flamme plate atmosphérique. Les résultats montrent que cet outil est opérationnel, répondant à un besoin pour l'amélioration des performances des systèmes de propulsion. / This PhD work is to develop a quantitative imaging technique for measurements of the concentration of pollutants in reactive flows. On one hand, the concern was to develop the NO fluorescence imaging technique. For this purpose, an n-level fluorescence model was first developed to calculate the behavior of fluorescence signals with temperature, species concentration, and pressure. Then this model was validated with fluorescence and absorption measurements acquired in an optical cell up to 800 K and to 20 bar and in a high-pressure laminar burner. From this model, a strategy used to measure the instantaneous NO distribution in a stratified flame was defined. Then, a similar study to detect CO with fluorescence was then investigated. Two-photon fluorescence measurements were performed in the optical cell and in a flame. The results make clear that the spectroscopic diagnostic becomes operational with the need to improve the performances of propulsion systems.

Laser flare can often be a major issue in particle image velocimetry (PIV) involving solid boundaries in a flow or a gas-liquid interface. The use of fluorescent light from dye-doped particles has been demonstrated in water applications, but reproducing the technique in an airflow is more difficult due to particle size constraints and safety concerns. The following thesis is formatted in a hybrid manuscript style, including a full paper presenting the applications of fluorescent Kiton Red 620 (KR620)-doped polystyrene latex microspheres in PIV. These particles used are small and monodisperse, with a mean diameter of 0.87 μm. The KR620 dye exhibits much lower toxicity than other common fluorescent dyes, and would be safe to use in large flow facilities. The first sections present a general introduction followed by a validation experiment using a standard PIV setup in a free jet. This work was the first to demonstrate PIV using fluorescent KR620-doped microspheres in an airflow, and results from the experiment were compared to similar data taken using standard PIV techniques. For the free jet results, Mie-scattered and fluorescent PIV were compared and showed average velocities within 3% of each other at the nozzle exit. Based on the PIV validation requirements used, this was deemed to be more of an indication of nozzle unsteadiness rather than an error or bias in the data. Furthermore, fluorescent PIV data obtained vector validation rates over 98%, well above the standard threshold of 95%. The journal article expands on the introductory work and analyzes testing scenarios where fluorescent PIV allows for velocity measurements much closer to a solid surface than standard, Mie-scattered PIV. The fluorescent signal from the particles is measured on average to be 320 ± 10 times weaker than the Mie scattering signal from the particles. This fluorescence-to-Mie ratio was found to be nonuniform, with the typical signal ratio for a single particle expected to fall between 120 and 870. This reduction in signal is counterbalanced by greatly enhanced contrast via optical rejection of the incident laser wavelength. Fluorescent PIV with these particles is shown to eliminate laser flare near surfaces, in one case leading to 63 times fewer spurious velocity vectors than an optimized Mie scattering implementation in a region more than 5 mm from an angled surface. In the appendix, a brief summary of an experiment to characterize the temperature sensitivity of the KR620 dye is included. This experiment concluded that the KR620 particles did not exhibit sufficient temperature sensitivity to warrant further investigation at the time. / Master of Science

Inductively coupled plasma-mass spectrometers (ICP-MS) have become the workhorses of many analytical labs over the past few decades. Despite the instruments' high sensitivities and low detection limits there is still a demand for improvements in several aspects of their performance. One area of improvement is in the understanding of "space charge effects" Space charge effects are classified as problems associated with the ion beam. Problems are created when the mutual repulsions of the ions make consistent focusing of the ion beam difficult. This is particularly problematic with samples containing a low concentration analyte contained within a high salt solution matrix, resulting in lower instrument sensitivity and inaccurate results. The research presented here used laser-induced fluorescence (LIF) imaging to characterize the ion beam as it enters the mass analyzer of a commercial ICP-MS. To perform the LIF imaging a laser system with two ring cavities was constructed to frequency double a CW titanium-sapphire laser to the calcium ion transition at 393.4 nm or to the barium ion transition at 455.4 nm. Ion beam images for both elements were taken under different instrument modes and matrix compositions. The same trends in shift and distortion of the barium ion beam with the addition of a lead matrix was observed as in previous experiments with calcium. A shift in the focal point of the ion beams of both elements was also observed in normal sensitivity mode and with the instrument's collisional reaction interface (CRI). This work indicates that a shift in beam focusing is responsible for the change in ion transmission due to changes in matrix composition and instrument modes.