Doctor of Philosophy / Department of Physics / Chii-Dong Lin / Imaging of molecules has always occupied an essential role in physical, chemical and biological sciences. X-ray and electron diffraction methods routinely achieve sub-angstrom spatial resolutions but are limited to probing dynamical timescales longer than a picosecond. With the advent of femtosecond intense lasers, a new imaging paradigm emerges in last decade based on laser-induced electron diffraction (LIED). It has been placed on a firm foundation by the quantitative rescattering theory, which established that large-angle e-ion elastic differential cross sections (DCS) can be retrieved from the LIED spectrum. We further demonstrate that atomic potentials can be accurately retrieved from those extracted DCSs at energies from a few to several tens of electron volts. Extending to molecules, we show mid-infrared (mid-IR) lasers are crucial to generate high-energy electron wavepackets (> 100 eV) to resolve the atomic positions in a molecule. These laser-driven 100 eV electrons can incur core-penetrating collisions where the momentum transfer is comparable to those attained in conventional keV electron diffraction. Thus a simple independent atom model (IAM), which has been widely used in conventional electron diffractions, may apply for LIED. We theoretically examine and validate the applicability of IAM for electron energies above 100 eV using e-molecule large-angle collision data obtained in conventional experiments, demonstrating its resolving powers for bond lengths about 0.05 angstrom. The Validity of IAM is also checked by an experimental LIED investigation of rare gas atoms in the mid-IR regime. We show that the electron’s high energy promotes core-penetrating collisions at large scattering angles, where the e-atom interaction is dominated by the strong short range atomic-like potential. Finally, we analyze the measured LIED spectrum of N[subscript]2 and O[subscript]2 at three mid-IR wavelengths (1.7, 2.0, and 2.3 μm). As expected, the retrieved bond lengths of N[subscript]2 at three wavelengths are about same as the equilibrium N[subscript]2 bond length. For O[subscript]2, the data is also consistent with a bond length contraction of 0.1 angstrom within 4-6 fs after tunnel ionization. This investigation establishes a foundation for this novel imaging method for spatiotemporal imaging of gas-phase molecules at the atomic scale.

Les exigences de plus en plus élevés concernant la qualité et propriétés de couches minces ont soutenu le développement de nouveaux procédés de pulvérisation. Ainsi, la décharge magnétron conventionnelle en courant continu, une des sources d’atomes la plus utilisée pour le dépôt de couches minces, a été améliorée par le couplage avec une décharge additionnelle de radio fréquence pour obtenir le nouveau procédé RF-IPVD (Radio Frequency-Ionized Physical Vapour Deposition). Ce procédé permet de générer un degré d’ionisation supérieur à celui dans la décharge magnétron classique, nécessaire pour contrôler les propriétés des couches minces. Un procédé alternatif pour augmenter d’avantage l’ionisation consiste à appliquer des impulsions haute puissance sur la cathode HPPMS (High Power Pulsed Magnetron Sputtering), pour des durés courtes de l’ordre de ųs ou dizaines de ųs. L’étude menée porte sur les phénomènes de pulvérisation et de transport des espèces du métal dans ces trois versions de la décharge magnétron par les moyens de spectroscopie laser à l’aide des diodes laser accordables. Le développement récent de ces diodes nous a permis de sonder les niveaux fondamentaux du Titane et de l’Aluminium, et de caractériser la dépendance spatiale de la densité et température ainsi que la fonction de distribution en vitesse de ces atomes. L’effet des paramètres clés, comme l’intensité du courant et la pression du gaz, est étudie et décrit pour la décharge magnétron conventionnelle. La distribution spatiale et angulaire de la fonction de distribution en vitesses a été mesurée dans la région devant la cible magnétron, afin de caractériser les flux du métal et leur comportement dans le volume de la décharge. L’étude sur les atomes du métal dans le procédé RF-IPVD est concentrée sur l’effet de la décharge additionnelle sur le dépeuplement du niveau fondamental. Une efficacité plus grande des processus d’ionisation est trouvée à plus haute pression et plus haute puissance RF injecté. On a montré aussi que les atomes affectés par les processus d’ionisation sont ceux thermalisées, tandis que la distribution de atomes rapides n’est quasiment pas affectés par la décharge additionnelle.Le diagnostic de la décharge pulsée a nécessité le développement d’une nouvelle procédure expérimentale, capable de suivre l’évolution de la densité et de la température des espèces neutres avec une résolution de l’ordre de la ųs. Cette procédure nous a servi pour décrire l’évolution spatio-temporel des atomes du métal (Ti et Al) et les atomes métastables d’Ar. Ces études offrent une vue globale sur le transport de atomes pulvérisés pendant la post décharge, ainsi qu’une description du fonctionnement de la décharge pulsé via la création des métastables d’Argon. / The higher requirements on the thin films quality have supported the development of new sputtering techniques. Thus, the conventional DC magnetron discharge, one of the most widely used source of atoms for thin film deposition, has been improved by the addition of an auxiliary radio frequency discharge - new technique called RF-IPVD (Radio Frequency -Ionized Physical Vapor Deposition). This technique highly increases the ionization degree compared to conventional magnetron discharge, which is necessary for a better control of the thin films properties. An alternative method to increase the ionization is based on the use of high power pulses on the cathode, HPPMS (High Power Pulsed Magnetron Sputtering), for short periods of time ranging from ųs to tens of ųs.The present study focuses on the sputtering phenomena and the transport of metal sputtered species in these three versions of the magnetron discharge, by means of laser spectroscopy using tunable laser diodes. The recent developments of these diodes have allowed to probe the fundamental levels of titanium and aluminum, and to characterize the spatial dependency of the density and temperature as well as the velocity distribution functions of these atoms. The effect of key discharge parameters, such as current intensity and gas pressure, is studied and described for the conventional magnetron discharge. The spatial and angular velocity distribution functions were measured in front of the magnetron target, in order to characterize the metal fluxes and their behavior in the discharge volume.The study on the metal atoms in the RF-IPVD process is focused on the effect of the additional discharge on the depopulation of the ground state level. Higher ionization efficiency is found at relatively high pressure and it increases with the injected RF power. It was also showed that the thermalized atoms are the ones involved in the ionization process, while the distribution of fast atoms is almost unaffected by the additional discharge.The diagnostics of the HPPMS discharge required the development of a novel experimental procedure, able to monitor the density and temperature of neutral species with a time resolution of ųs. This procedure was used to describe the spatiotemporal evolution of metal atoms (Ti and Al) and Ar metastable atoms. These studies provide an overview on the transport of sputtered atoms during the afterglow, and a description of the pulsed discharge operation, via the creation of metastable argon atoms.

Nos últimos anos, a Espectrometria de Emissão Atômica com Plasma induzido por Laser (LIBS) vem despertando grande interesse e pesquisas voltadas às aplicações analíticas dessa técnica tem aumentado significativamente. No entanto, sua aplicação na análise de amostras líquidas não é trivial, podendo haver comprometimento na sensibilidade e na precisão do método. Além disso, a análise quantitativa é considerada o \"calcanhar de Aquiles\" da técnica, especialmente devido à falta de materiais de referência certificados e à forte interferência de matriz. Nesse contexto, com a intenção de viabilizar a análise de matrizes líquidas por LIBS, esse trabalho propõe o uso de cerâmica como fase sólida para extração, pré-concentração e especiação de Cr em amostras de água. Foi realizado também um estudo de otimização dos parâmetros instrumentais do LIBS para o desenvolvimento de um método de medição de Cr na fase sólida, empregando cerâmica enriquecida com concentrações crescentes desse analito como material calibrante sintético. Os resultados obtidos mostraram que a cerâmica adsorve seletivamente a espécie Cr(III) em pH 7, sendo este um processo rápido, de baixo custo, cuja eficiência é pouco afetada pela presença de outros eletrólitos. Os estudos relacionados à otimização dos parâmetros instrumentais do LIBS indicaram que um diâmetro de focalização de 65 µm, um tempo de atraso de 0,75 µs, a energia por pulso de 20 mJ, uma taxa de repetição de 10 Hz e um número de pulsos igual a 403 podem ser recomendados para a quantificação de Cr no material cerâmico. Nessas condições, obteve-se uma curva de calibração analítica que possibilitou a medição Cr adsorvido em cerâmica. Uma amostra de água de torneira foi então enriquecida com 0,9 mg L-1 de Cr(III) e 0,9 mg L-1 de Cr(VI) para que um teste de recuperação fosse realizado com a finalidade de se verificar a aplicabilidade do método proposto, foi possível constatar a adsorção seletiva da espécie Cr(III), com recuperação de 105±2%. A quantificação da espécie Cr(VI) por LIBS também é possível após a redução dessa espécie a Cr(III) utilizando Fe(II) como agente redutor. Os limites de detecção (LOD) e quantificação (LOQ) estimados para o método foram respectivamente 21 mg kg-1 e 70 mg kg-1, equivalentes a 0,1 mg L-1 e 0,35 mg L-1, considerando-se o coeficiente de pré-concentração igual a 200 (m/m). / In recent years, Laser Induced Breakdown Spectroscopy (LIBS) has deserved attention of scientific community and researches using this technique have increased significantly. However, its application in the analysis of liquid samples is not trivial, because the sensitivity and accuracy of the method can be affected. In addition the quantitative analysis is considered the \"Achilles\' heel\" of the technique, especially due to the lack of certified reference materials and to the strong interference matrix. To enable the analysis of liquid matrices by LIBS, this work proposes the use of ceramic as solid phase in the extraction, preconcentration and speciation of Cr in water samples. LIBS instrumental parameters were also optimized to allow the measurement of Cr in this solid phase, for the development of a method for measuring the analyte in the solid phase, which was also used as synthetic calibrating material by the addition of increasing concentrations of the analyte. Results showed the ceramic selectively adsorbs Cr(III) species at pH 7, which is a low cost and rapid process, whose efficiency is not significantly affected by the presence of other electrolytes. Studies related to the optimization of LIBS instrumental parameters indicated that spot size of 65 µm, delay time of 0,75 µs , energy per pulse of 20 mJ, repetition rate of 10 Hz and a number of pulses equal to 403 can be recommended for the quantification of Cr the ceramic material. Under these conditions, it was obtained an analytical calibration curve which allowed a Cr measurement in ceramics. A tap water sample was enriched with 0.9 mg L-1 of Cr(III) and 0.9 mg L-1 of Cr (VI) and a recovery test was done in order to verify the applicability of the proposed method. It was observed the selective adsorption of the Cr(III) species, with recovery of 105 ± 2 %. The quantification of Cr(VI) species by LIBS was also possible, after reduction of this species to Cr(III) using Fe(II) as reducing agent. The limit of detection (LOD) and the limit of quantification (LOQ) obtained by the proposed method were respectively, 21 mg kg-1 and 70 mg kg-1, equivalent to 0.1 mg L-1 and 0.35 mg L-1, considering the preconcentration coefficient of 200 (on a w/w basis).

The concurrent spreading of a boundary layer type diffusion flame is studied. The impossibility of obtaining a low velocity laminar flow without any perturbation induced by buoyancy has lead to the development of an experimental apparatus for use in micro-gravity facilities. Based on previous experimental observations, an original numerical approach has been developed showing, first the dominating role of the radiative heat transfer on the structure of the flame and second the major role of the soot on the extinction phenomenon at the flame trailing edge. The influence of the forced flow velocity, the fuel injection velocity and oxygen concentration on the geometry of the flame has been examined by imaging of CH* and OH* radicals spontaneous emission. Laser-Induced Incandescence (LII) is used to determine the soot field concentration in the flame. The soot formation has been studied by Laser Induced Fluorescence (LIF) of Polycyclic Aromatic Hydrocarbons (PAHs). The interaction between the reaction zone and the field of soot formation/oxidation is taken into account to analyze the flame length. These results can be used as the experimental input data for a future complete validation of numerical model simulating the soot formation and oxidation in this kind of flame.

Ce travail contribue à la quasi-in-situ détection des nanoparticules par la technique d’incandescence induite par laser (LII) pendant le dépôt chimique en phase vapeur avec catalyseur flottant (FCCVD) de nanotubes de carbone. Premièrement, la microscopie électronique en transmission (MET) à haute résolution était utilisé pour caractériser la nature et la taille des nanoparticules. Le signal théorique de LII a été simulé en considérant la densité des nanoparticules, la capacité thermique et la distribution de taille, etc. La sensibilité et l’incertitude concrètes des paramètres clés sur la taille évaluée des particules pour ce modelé ont été estimées. Le modèle LII a été validé par la comparaison des résultats évalués avec ceux obtenus par la MET. Ensuite, la technique mature LII combinée avec MET a été appliquée pour étudier l’évolution des nanoparticules dans la phase gazeuse le long de l’axe du réacteur. L’influence de la température, de la concentration de ferrocène, de la source de carbone et de la proportion hydrogène sur la taille des nanoparticules a également été démontrée. Enfin, les rôles des nanoparticules dans la phase gazeuse au cours du processus de synthèse des NTC ont été discutés en corrélant les informations sur l’évolution axiale des nanoparticules et la morphologie des NTC synthétisés sur le substrat le long de l’axe du réacteur. Un modèle basé sur la thermodynamique de la nucléation des nanoparticules a été proposé pour décrire le processus de formation des nanoparticules au cours du processus DCVCF. Il est constaté que les nanoparticules asformé en phase gazeuse présentent des structures cœur-coquille avec un noyau de α-Fe et la coque de carbone. Ainsi, les nanoparticules de fer en phase gazeuse ne pourraient pas contribuer à la croissance de NTC sur le substrat à cause de l’encapsulation de carbone. En même temps, la taille des nanoparticules évaluée par LII est en bon accord avec celle-ci déterminée par MET. Cette étude, montrant les relations potentielles entre les nanoparticules flottantes et les NTCs sur le substrat, révèle une perspective importante de l’application de LII pour comprendre et améliorer le processus DCVCF. / This work contributes to the quasi-in-situdetection of nanoparticles by laser induced incandescence(LII) technique during the floating catalytic chemicalvapor deposition (FCCVD) synthesis of Carbonnanotubes.First, high resolution transmission electron microscopy(TEM) was used to characterize the nanoparticlenature and size. The theoretical LII signal was simulatedby considering the nanoparticle density, heatcapacity and size distribution, etc. A detailed sensitivityand uncertainty of the key parameters on the evaluatedparticle size for this model was estimated. TheLII model was validated by a comparison of the evaluatedresults with the ones obtained by TEM measurements.Then, the developed LII technique combinedwith TEM was applied to investigate the evolutionof nanoparticles in the gas phase along thereactor axis. The influence of the temperature, ferroceneconcentration, carbon source and hydrogen ratioon the nanoparticle size was also demonstrated. Finally,the roles of nanoparticles in the gas phase duringCNT synthesis process were discussed by correlatinginformation on the axial nanoparticle evolutionand the morphology of CNTs synthesized on thesubstrate along the reactor axis. And a model basedon the thermodynamics of the nanoparticle nucleationwas proposed to describe the nanoparticle formationprocess during the FCCVD process. It is found thatthe as-formed nanoparticles in the gas phase exhibitcore-shell structures with an α-Fe core and a carbonshell. Hence iron nanoparticles in the gas phasecould not contribute to the CNT growth on the substratebecause of the carbon encapsulation. Meanwhilethe evaluated size of nanoparticles by LII is ingood agreement with the TEM determined one. Thisstudy, showing potential relations between the floatingnanoparticles and the CNTs on the substrate, revealsthe important LII application prospect to understandand to improve the FCCVD process.

Cette thèse porte sur l'endommagement laser de composants optiques en silice amorphe en régime nanoseconde. Ce matériau diélectrique est l'un des plus couramment utilisés en optique et notamment sur des installations laser de haute énergie telles que le Laser MégaJoule. Afin de garantir le fonctionnement nominal d'une installation, l'endommagement laser des composants optiques doit être compris et maîtrisé. Ce phénomène induit une modification irréversible du matériau modifiant la propagation du faisceau. Dans le régime nanoseconde, l'endommagement laser de la silice est corrélé à la présence de défauts précurseurs qui sont une conséquence de la synthèse et du polissage des composants. L'interaction de ces précurseurs avec le laser va dépendre des caractéristiques de ce dernier. Une première étude est consacrée à la métrologie des impulsions utilisées en laboratoire pour étudier l'endommagement laser. Une seconde étude porte sur les mécanismes d'amorçage des dommages sur la face de sortie des composants optiques faits de silice. Une dernière partie porte sur l'influence de la propagation non linéaire sur l'endommagement surfacique et volumique des composants épais faits de silice. / In this thesis, laser-induced damage phenomenon in fused silica components is investigated in the nanosecond regime. This material is one of the most widely used in optics, particularly on high-energy laser facilities such as the Laser MégaJoule. In order to ensure the nominal operation of this kind of laser facility, laser-induced damage on optical components has to be understood and controlled. This phenomenon consists in an irreversible modification of the material. In the nanosecond regime, laser-induced damage is tightly correlated to the presence of precursor defects which are a consequence of the synthesis and the polishing of the components. The interaction between these precursor defects and the laser pulses strongly depends on the laser characteristics. The first study focuses on the metrology of the laser beam used in laboratory to study laser-induced damage. The second one consists in a parametric study of the initiation mechanism on the rear surface of fused silica components. The last part deals with the influence of nonlinear propagation on laser induced damage on the surface and in the volume of thick fused silica samples.

A UV Laser Induced Fluorescence (LIF) system, previously developed in our laboratory, was modified and used for a series of applications related to the development and optimization of UV LIF spectroscopic measurements of trace contaminants in drinking water and other water sources. Fluorescence spectra of a number of water samples were studied, including those related to the reverse osmosis water treatment and membrane fouling, domestic and international drinking water, industrial toxins, bacterial spores, as well as several fluorescence standards. Of importance was that the long term detection of the trace level of Dissolved Organic Compounds (DOC) was measured, for the first time to our knowledge, over a one week period and with a time resolution of 2.5 minutes. A comparison of LIF emission using both 266 nm and 355 nm excitation was also made for the first time. Such real-time and continuous measurements are important for future water treatment control. The LIF system was modified to accommodate UV Light Emitting Diodes (LED) as alternative excitation sources, and tested for the detection of trace organic species in water. In addition, a compact system using LED excitation and a spectrometer was xviii developed and underwent initial testing. The original LIF system had two laser sources, 266 nm and 355 nm. The additional sources incorporated in the system were UV LEDs emitting at 265 nm, 300 nm, 335 nm and 355 nm. The LED spectral emission was studied in detail, in terms of spectral variability and power output. It was found that all LEDs had some emission in the visible spectrum, and an optical filter was used to remove it. The signal-to-noise ratio for the LED-based systems was determined and compared with that of the LIF system. The fluorescent signal of the LED-based system was smaller by 1 to 2 orders of magnitude, despite the fact that the LED pulse energy was 2 to 3 orders of magnitude less than the laser's. As such, the fluorescent signal from the LED was greater than expected. Therefore, a UV LED may be a compact and much cheaper optical source for future water measurement instruments.

Over the last decade our understanding of mercury cycling has dramatically changed. Evidence of rapid atmospheric oxidation has been observed in the Arctic, Antarctic, the MBL, coastal environments, saline lakes, and the upper troposphere/lower stratosphere. These results show that, Hg0, can undergo rapid gas-phase oxidation under standard atmospheric conditions. However, the mechanism and importance of this transformation is still unclear. The goal of this work was two-fold: to investigate of the kinetics of potential pathway for the gas phase oxidation of atmospheric mercury and to develop new laser based techniques, which can be employed for both laboratory and field studies of Hg(0) and the products of mercury oxidation. First and foremost, this work determined kinetic rate coefficients for the potentially important mercury reactions. Rate coefficients were determined using a Pulse Laser Photolysis - Laser Induced Fluorescence (PLP-LIF) technique monitoring one or more of the following species, Hg(0), Cl, Br, HgCl, and HgBr. The concentrations of these species were measured by LIF as the reaction occurred and a concentration vs. time profile was generated. From these profiles a rate coefficient for the reaction can be obtained. In the course of this work kinetic rate coefficients for the following mercury reactions were measured. Hg(0) + Cl + M --> HgCl + M Hg(0) + Br + M --> HgBr + M HgBr + M --> Hg(0) + Br + M HgBr + Br --> products HgCl + O2 --> products This work is the first direct measurement of a kinetic rate coefficient for these reactions, and the first work which employed one photon LIF to monitor the HgCl and HgBr products. The second aspect of this work was the development of new laser based techniques to detect atmospheric mercury and its oxidation products for both laboratory and field application. In this work a LIF technique was develop to detect HgCl and HgBr. In addition, a two photon LIF technique initially developed by Bauer et al., 2002 was verified and expanded. The two photon LIF technique was used to directly monitor Hg(0) atoms in-situ, to monitor Hg(0) evolving form a gold tube, and to monitor the Hg(0) evolving from the thermal decomposition of reactive gaseous mercury collected on a KCl coated or uncoated denuder. This work represents a significant advance in the development of a viable method the detect mercury and the mercury oxidation products in the laboratory and in the field and is the first study to observe clear differences in the characteristic desorption profiles of HgO and HgX2. This work has broad implications, it enhanced our current knowledge concerning the biogeochemical cycling of mercury, broadened our understanding of the mercury chemistry in high halogen environment, and provided new techniques which can be applied in future field and laboratory studies.

Fuel-air mixing enhancement in axisymmetric jets using an array of synthetic jet actuators around the perimeter of the flows (primarily parallel to the flow axis) was investigated using planar laser-induced fluorescence of acetone. The synthetic jets are a promising new mixing control and enhancement technology with a wide range of capabilities. An image correction scheme that improved on current ones was applied to the images acquired to generate quantitative mixing measurements. Both a single jet and coaxial jets were tested, including different velocity ratios for the coaxial jets. The actuators run at a high frequency (~1.2 kHz), and were tested with all of them on and in other geometric patterns. In addition, amplitude modulation was imposed at a lower frequency (10-100 Hz). The actuators generated small-scale structures in the outer (and inner, for the coaxial jets) mixing layers. These structures significantly enhanced the mixing in the near field (x/D less than 1) of the jets, which would be useful for correcting an off-design condition in a combustor. The amplitude modulation generated large-scale structures that became apparent farther downstream (x/D greater than 1). The impulse at the start of the duty cycle was responsible for creating the structures. The large structures contained broad regions of uniformly mixed fluid, and also entrained fluid significantly. In addition, highly asymmetric forcing geometries displayed the power of the actuators to control the spatial distribution of jet fluid. This spatial control is important for the correction of hot spots in the pattern factor. In order to extend quantitative acetone PLIF to two-phase flows, the remaining unknown photophysical properties of acetone were identified. Tests showed that the technique could simultaneously capture acetone vapor and acetone droplets. A model of droplet fluorescence was developed, and applied to images acquired in a dilute spray. The sensitivity of the model to the value of the unknowns was evaluated, including a best and worst case. The results revealed that several liquid acetone photophysical properties must be measured for the further development of the technique, especially the phosphorescence yield. Quantitative two-phase acetone PLIF will provide a powerful new tool for studying spray flows.

Thermal management challenges for microelectronics are a major issue for future integrated circuits, thanks to the continued exponential growth in component density described by Moore¡¯s Law. Current projections from the International Technology Roadmap for Semiconductors predict that local heat fluxes will exceed 1 kW/cm2 within a decade. There is thus an urgent need to develop new compact, high heat flux forced-liquid and evaporative cooling technologies. Thermometry techniques that can measure temperature fields with micron-scale resolution without disturbing the flow of coolant would be valuable in developing and evaluating new thermal management technologies. Specifically, the ability to estimate local convective heat transfer coefficients, which are proportional to the difference between the bulk coolant and wall surface temperatures, would be useful in developing computationally efficient reduced-order models of thermal transport in microscale heat exchangers. The objective of this doctoral thesis is therefore to develop and evaluate non-intrusive optical thermometry techniques to measure wall surface and bulk liquid temperatures with O(1-10 micronmeter) spatial resolution. Intensity-based fluorescence thermometry (FT), where the temperature distribution of an aqueous fluorescent dye solution is estimated from variations in the fluorescent emission intensity, was used to measure temperatures in steady Poiseuille flow at Reynolds numbers less than 10. The flow was driven through 1 mm square channels heated on one side to create temperature gradients exceeding 8 ¡ÆC/mm along both dimensions of the channel cross-section. In the evanescent-wave fluorescence thermometry (EFT) experiments, a solution of fluorescein was illuminated by evanescent waves to estimate the solution temperature within about 300 nm of the wall. In the dual-tracer FT (DFT) studies, a solution of two fluorophores with opposite temperature sensitivities was volumetrically illuminated over most of the `cross-section of the channel to determine solution temperatures in the bulk flow. The accuracy of both types of FT is determined by comparing the temperature data with numerical predictions obtained with commercial computational fluid dynamics software. The results indicate that EFT can measure wall surface temperatures with an average accuracy of about 0.3 ¡ÆC at a spatial resolution of 10 micronmeter, and that DFT can measure bulk water temperature fields with an average accuracy of about 0.3 ¡ÆC at a spatial resolution of 50 micronmeter in the image plane. The results also suggest that the spatial resolution of the DFT data along the optical axis (i.e., normal to the image plane) is at least an order of magnitude greater than the depth of focus of the imaging system.