Dissertations / Theses on the topic 'SATURATED-ABSORPTION CAVITY RING-DOWN SPECTROSCOPY'

La spectroscopie d'absorption moléculaire est un outil incontournable non seulement pour la physique fondamentale et la métrolgie mais aussi pour des domaines aussi divers que les sciences environnementales, la planétologie ou l'astrophysique. Ces dernières années, des techniques spectroscopiques qui exploitent l'amplification résonnante d'interaction entre lumière laser et molécules dans une cavité optique ont fourni des détectivités exceptionnelles sur l'axe d'absorption, tandis que l'axe de fréquence des spectromètres n'atteignait généralement pas le même niveau de précision.Dans cette thèse, nous avons répondu à ce défi en développant la spectroscopie en cavité par temps de déclin stabilisée en fréquence par rétroaction optique (OFFS-CRDS en anglais). Cette nouvelle technique présente une combinaison unique de stabilité et résolution fréquentielles sub-kHz, d'un niveau d'intensité lumineuse intra-cavité de l'ordre du kW/cm^2, d'une detectivite de 2 x 10^(−13) cm^(−1)Hz^(-1/2) limitée par le bruit de photons, et d'une limite de détection de 8.4 x 10^(−14) cm^(−1) sur une plage spectrale étroite. Ces performances inédites sont dues à l'asservissement de la cavité spectroscopique à un laser balayé en fréquence par modulation à bande latérale unique et stabilisé par rétroaction optique avec une cavité en V de réference ultrastable. Pour transférer la cohérence de ce laser sub-kHz à des lasers plus bruiteux dans d'autres gammes spectrales à travers un peigne de fréquence optique, nous avons exploré une nouvelle méthode de clonage de phase par une correction anticipative à large bande passante et démontré une erreur résiduelle de phase de 113 mrad. En appliquant l'OFFS-CRDS à la spectroscopie du CO2 à 1.6 μm, nous avons obtenu un spectre large bande avec une dynamique de 8 x 10^5, et nous avons déterminé douze fréquences de transition absolues avec une exactitude de l'ordre du kHz en mesurant des Lamb dips sub-Doppler en absorption saturée avec un dispositif équipé d'un peigne de fréquence. Par ailleurs, nous avons procédé à une analyse détaillée des sources d'erreurs systematiques en CRDS et nous avons déduit une formule analytique pour le déclin de cavité non-exponentiel dans un régime faiblement saturé qui est susceptible de contribuer à de futures mesures de moments de transition dipolaire indépendantes de la concentration. Nos résultats ouvrent des perspectives prometteuses pour des applications métrologiques de l'OFFS-CRDS, comme par exemple l'étude de profils de raie poussés, la mesures de rapports isotopiques et la spectroscopie d'absorption saturée extensive dans le proche infrarouge
High-precision molecular absorption spectroscopy is a powerful tool for fundamental physics and metrology, as well as for a broad range of applications in fields such as environmental sciences, planetology and astrophysics. In recent years, spectroscopic techniques based on the enhanced interaction of laser light with molecular samples in high-finesse optical cavities have provided outstanding detection sensitivities on the absorption axis, while the spectrometer frequency axis rarely met as high precision standards.In this thesis, we addressed this challenge by the development of Optical Feedback Frequency-Stabilized Cavity Ring-Down Spectroscopy (OFFS-CRDS). This novel technique features a unique combination of sub-kHz frequency resolution and stability, kW/cm^2-level intracavity light intensity, a shot-noise limited absorption detectivity down to 2 x 10^(−13) cm^(−1)Hz^(-1/2), as well as a detection limit of 8.4 x 10^(−14) cm^(−1) on a narrow spectral interval. This unprecedented performance is based on the tight Pound-Drever-Hall lock of the ring-down cavity to a single-sideband-tuned distributed-feedback diode laser which is optical-feedback-stabilized to a highly stable V-shaped reference cavity. To transfer the coherence of this sub-kHz laser source to noisier lasers in other spectral regions through an optical frequency comb, we have explored a novel high-bandwidth feed-forward phase cloning scheme and demonstrated a residual phase error as low as 113 mrad. Applying OFFS-CRDS to the spectroscopy of CO_2 near 1.6 μm, we obtained a broadband spectrum with a dynamic range of 8 x 10^5 and retrieved twelve absolute transition frequencies with kHz-accuracy by measuring sub-Doppler saturated absorption Lamb dips with a comb-assisted setup. Furthermore, we have performed a comprehensive analysis of systematic error sources in CRDS and derived an analytic formula for the non-exponential ring-down signal in a weakly saturated regime, which may contribute towards future concentration-independent transition dipole moment measurements. Our results open up promising perspectives for metrological applications of OFFS-CRDS, such as advanced absorption lineshape studies, isotopic ratio measurements and extensive saturated absorption spectroscopy in the near infrared

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Tese (Doutoramento)
IPEN/T
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

Les processus de combustion, qui representent aujourd'hui notre principal source d'energie, suscitent encore de nombreuses interrogations. Cela tient essentiellement a la complexite des mecanismes chimiques mis en jeu ainsi qu'a la difficulte inherente a l'etude d'un milieu qui est le sein de plusieurs milliers de reactions simultanees. Or, meme si des modeles performants permettent la simulation de systemes chimiques complexes, ils ne peuvent predire n'importe quels processus de combustion et l'approche experimentale de ceux-ci reste essentielle pour l'amelioration des modeles existant. En particulier, la mesure quantitative d'especes minoritaires dans les flammes constitue une etape fondamentale dans la validation des mecanismes chimiques a haute temperature. C'est dans cette optique que nous avons developpe une nouvelle technique pour l'etude de flamme, le cavity ring-down spectroscopy (crds). Cette technique, qui s'apparente a une methode d'absorption de tres haute sensibilite et dont le principe est base sur la mesure du temps de vie d'une impulsion laser injectee dans une cavite optique dans laquelle se trouve un echantillon absorbant, est apparue a la fin des annees 80 (o'keefe et deacon 1988) dans le cadre d'une etude spectroscopique
Dans ce memoire, nous montrons l'interet et les potentialites du crds pour l'etude de flammes homogenes. Pour ce faire, nous explicitons dans le detail le principe du crds et les precautions a prendre pour la mesure de concentrations absolues. Par ailleurs, une comparaison des profils de concentration absolue obtenus par crds (de cn et ch notamment) dans une flamme de ch 4/o 2 dopee en no, avec ceux issus de la modelisation au moyen du logiciel premix est egalement presentee. Le tres bon accord de cette comparaison montre que le crds, de part sa haute sensibilite et son caractere quantitatif direct, se revele etre une methode des plus efficaces pour la mesure de concentrations absolues d'especes dans des flammes homogenes

Un spectromètre utilisant la technique CRDS a été développé entre 2.00 et 2.35 µm afin de réaliser la spectroscopie en absorption de molécules d’intérêt atmosphérique et planétologique avec une très grande sensibilité et à haute résolution spectrale. Cette région du spectre correspond à une fenêtre de transparence de la vapeur d’eau et du dioxyde de carbone. Ces fenêtres sont des zones de très faible absorption utilisées pour le sondage des atmosphères terrestre et vénusienne dans lesquelles la vapeur d’eau et le dioxyde de carbone représentent respectivement les absorbants gazeux principaux dans l’infrarouge.La technique CRDS consiste à injecter des photons dans une cavité optique de haute finesse et à mesurer la durée de vie des photons dans cette cavité. Celle-ci est mesurée en interrompant l’injection des photons dans la cavité optique lors du passage en résonance du laser avec l’un des modes longitudinaux. Cette durée de vie dépend de la réflectivité des miroirs et des pertes intra-cavité comme celles induites par un gaz qui absorbe. Mesurer ces pertes en fonction de la longueur d’onde permet d’obtenir le spectre d’absorption du gaz en question. L’extrême réflectivité des miroirs permet d’atteindre dans une cavité d’un peu plus d’1 m de longueur une sensibilité équivalente à celle qui serait obtenue classiquement avec une cellule d’absorption longue de plusieurs milliers de kilomètres.Trois diodes laser DFB émettant autour de 2.35, 2.26 et 2.21 µm ont été utilisées avec ce spectromètre. Grâce à une rétro-action optique provenant d’une cavité externe, certaines de ces diodes ont pu être affinées, ce qui a permis de mieux injecter la cavité haute finesse et ainsi de réduire le niveau de bruit du spectromètre. Parallèlement grâce à une collaboration avec l’Institut d’Electronique (IES, UMR 5214) à Montpellier et la société Innoptics nous avons pu tester le prototype d’un VECSEL (Vertical-External-Cavity Surface-Emitting-Laser). Ce laser a permis de couvrir une gamme spectrale de 80 cm-1, entre 4300 et 4380 cm-1, équivalente à quatre diodes laser DFB. La sensibilité obtenue en routine avec ce spectromètre, correspondant au coefficient minimum détectable, est typiquement de 1×10-10 cm-1. Le chapitre introductif (Chapitre 1) fait le point sur les différentes techniques permettant d’acquérir des spectres en absorption dans la gamme spectrale étudiée et sur les sensibilités atteintes. A notre connaissance l’instrument développé ici est le plus sensible dans cette région du spectre. Le fonctionnement de ce spectromètre CRDS est détaillé dans le chapitre 2.Pour démontrer les performances obtenues avec notre instrument celui-ci a été utilisé pour enregistrer des transitions quadrupolaires donc de très faible intensité. Ainsi la transition S(3) de la bande 1–0 de HD a été enregistrée pour la première fois et son intensité mesurée (S=2.5×10-27 cm/molecule). La sensibilité obtenue en routine a encore pu être améliorée en réalisant une moyenne d’une centaine de spectres sur une gamme spectrale réduite pour atteindre 1×10-11 cm-1. Grâce à cela nous avons pu mesurer la position et l’intensité de la raie quadrupolaire électrique O(14) de la bande 2–0 de N2 qui est très fortement interdite avec une intensité de 1.5×10-30 cm/molecule. Ces mesures font l’objet du chapitre 3 de cette thèse.Les deux derniers chapitres sont dédiés à la caractérisation de l’absorption du CO2, au centre de la fenêtre de transparence, et à celle de la vapeur d’eau. Dans les deux cas, les transitions permises du monomère et la contribution du continuum ont été étudiées. Ce dernier correspond à une absorption variant lentement avec la longueur d’onde. Les sections efficaces du « self-continuum » de la vapeur d’eau ont notamment été mesurées en plusieurs points de la fenêtre de transparence avec une incertitude beaucoup plus faible que les mesures existantes. Elles représentent un jeu de données décisif pour tester les modèles décrivant ce continuum
A cavity ring down spectrometer has been developed in the 2.00-2.35 µm spectral range to achieve highly sensitive absorption spectroscopy of molecules of atmospheric and planetologic interest and at high spectral resolution. This spectral region corresponds to a transparency window for water vapor and carbon dioxide. Atmospheric windows, where absorption is weak, are used to sound the Earth’s and Venus’ atmospheres where water vapor and carbon dioxide represent the main gaseous absorbers in the infrared, respectively.The CRDS technique consists of injecting photons inside a high finesse optical cavity and measuring the photon’s life time of this cavity. This life-time depends on the mirror reflectivity and on the intra-cavity losses due to the absorbing gas in the cavity. Measuring these losses versus the wavelength allow obtaining the absorption spectrum of the gas. The extreme reflectivity of the mirrors allows reaching, for a 1-meter long cavity, a sensitivity equivalent to the one obtained classically with absorption cells of several thousands of kilometers.Three DFB laser diodes emitting around 2.35, 2.26, 2.21 µm were used with this spectrometer giving access to the 4249-4257, 4422-4442 and 4516-4534 cm-1 interval, respectively. Thanks to optical feedback from an external cavity, two of these diodes were spectrally narrowed leading to a better injection of the high finesse cavity thus reducing the noise level of the spectrometer. In parallel, we tested a VECSEL (Vertical-external-Cavity, Surface Emitting laser) through a collaboration with the Institu d’Electronique (IES, UMR 5214) in Montpellier and the Innoptics firm. This laser source is able to cover a 80 cm-1 spectral range centered at 4340 cm-1, equivalent to four DFB laser diodes. In routine the achieved sensitivity with this spectrometer, corresponding to the minimum detectable coefficient is typically of 1×10-10 cm-1. The introductive chapter (Chapter 1) makes the point on the different techniques allowing absorption spectra recordings in the studied spectral region and on their sensitivity. The experimental set-up, the characteristics and performances by the CRD spectrometer developed in this work are detailed in Chapter 2. To our knowledge this instrument is the most sensitive in the considered spectral region.In Chapter 3, detection of quadrupolar electric transitions of HD and N2 illustrate the level of sensitivity reached: (i) the S(3) transition in the 1-0 band of HD has been recorded for the first time and its intensity measured (S=2.5×10-27 cm/molecule), (ii) the position and intensity of the highly forbidden O(14) quadrupolar electric transition of the 2-0 band of N2 have also been newly determined.The two last chapters are devoted to the characterization of the CO2 absorption, in the centre of the transparency window, and of the water vapor absorption. In both cases, we not only studied the allowed transitions of the monomer, but also the continuum absorption. This latter correspond to a weak background absorption varying slowly with the wave length. The self-continuum cross-sections of the water vapor continuum were measured in many spectral points through the transparency window with a much better accuracy compared to existing measurements. These CRDS data constitute a valuable data set to validate the reference model (MT_CKD) for the continuum which is implemented in most of the atmospheric radiative transfer codes

The real-time detection of trace species is key to a wide range of applications such as on-line chemical process analysis, medical diagnostics, identification of environmentally toxic species and atmospheric pollutant sensing. There is a growing demand for suitable techniques that are not only sensitive, but also simple to operate, fast and versatile. Most currently available techniques, such as spectrophotometry, are neither sensitive enough nor fast enough for kinetic studies, whilst other techniques are too complex to be operated by the non-specialist. This thesis presents two techniques that have been developed for and applied to liquid-phase analysis, with supercontinuum (SC) radiation used for liquid-phase absorption for the first time. Firstly, supercontinuum cavity enhanced absorption spectroscopy (SC-CEAS) was used for the kinetic measurement of chemical species in the liquid phase using a linear optical cavity. This technique is simple to implement, robust and achieves a sensitivity of 9.1 × 10−7 cm−1 Hz−1/2 at a wavelength of 550nm for dye species dissolved in water. SC-CEAS is not calibration-free and for this purpose a second technique, a time-resolved variant called broadband cavity ring-down spectroscopy (BB-CRDS), was successfully developed. Use of a novel single-photon avalanche diode (SPAD) array enabled the simultaneous detection of ring-down events at multiple spectral positions for BB-CRDS measurements. The performance of both techniques is demonstrated through a number of applications that included the monitoring of an oscillating (Belousov-Zhabotinsky) reaction, detection of commercially important photoluminescent metal complexes (europium(III)) at trace level concentration, and the analysis of biomedical species (whole and lysed blood) and proteins (amyloids). Absorption spectra covering the entire visible wavelength range can be acquired in fractions of a second using sample volumes measuring only 1.0mL. Most alternative devices capable of achieving similar sensitivity have, up until now, been restricted to single wavelength measurements. This has limited speed and number of species that can be measured at once. The work presented here exemplifies the potential of these techniques as analytical tools for research scientists, healthcare practitioners and process engineers alike.

The work presented in this thesis is predicated upon the environmental applications of cavity enhanced absorption spectroscopy and cavity ring-down spectroscopy. These are related techniques that are highly useful for sensitive gas detection which is important in terms of anthropologically induced climate change and the detection of the changing levels of greenhouse gases. Sensitive gas detection techniques, specifically isotope ratio analysis, are useful for determining the sources and sinks of greenhouse gases and for distinguishing whether sources and sinks are natural or anthropogenic. The research involved gas detection using commercial near-infrared cavity ring-down spectrometers, made by Picarro, and highlights how well and to what environmental uses these instruments can be applied. Various gas mixtures containing methane and carbon dioxide were analysed by the CRDS instruments to try to determine the detection limits, and the effect that varying the concentrations would have upon the precision and accuracy of the measurements made. Headspace soil measurements of CH4 and C02 were also demonstrated to be made easily without processing of the gas stream.The main work described in this Thesis involved the implementation of a home-built optical feedback cavity enhanced absorption spectroscopy /cavity ring-down spectroscopy experiment which made use of a V-shaped optical cavity and a 7.8 υm quantum cascade laser for the detection of greenhouse gases in the mid-infrared. This comprised of the detection and analyses of spectral lines of methane and nitrous oxide isotopologues. Measurement in the mid-IR took advantage of the excitation of the stronger fundamental vibrational transitions occurring in this region and increased optical path lengths from the optical cavity and signal amplification from optical feedback are features that gave high signal to noise measurements. These techniques have the potential to be further developed for field usage by overcoming many of the limitations of alternative greenhouse gas detection techniques, such as instrument sensitivity and portability.

Detailed investigations of molecular collisions at the gas-surface interface provide insight into the dynamics and mechanisms of important interfacial reactions. A thorough understanding of the fundamental interactions between a gas and surface is crucial to the study of heterogeneous chemistry of atmospheric organic aerosols. In addition to changing the chemical and physical properties of the particle, reactions with oxidizing gases may alter aerosol optical properties, with implications for the regional radiation budget and climate. Molecular beams of CO₂, NO₂ and O₃ were scattered from long-chain methyl (CH₃-), hydroxyl (OH-), vinyl (H₂C=CH-) and perfluorinated (CF₃(CF₂)₈-, or F-) ω-functionalized alkanethiol self-assembled monolayers (SAMs) on gold, to explore the reaction dynamics of atmospherically important triatomics on proxies for organic aerosols. Energy exchange and thermal accommodation during the gas-surface collision, the first step of most interfacial reactions, was probed by time-of-flight techniques. The final energy distribution of the scattered molecules was measured under specular scattering conditions (θi = θf = 30°). Overall, extent of energy transfer and accommodation was found to depend on the terminal functional group of the SAM, incident energy of the triatomics, and gas-surface intermolecular forces. Reaction dynamics studies of O3 scattering from H2C=CH-SAMs revealed that oxidation of the double bond depend significantly on O₃ translational energy. Our results indicate that the room-temperature reaction follows the Langmuir-Hinshelwood mechanism, requiring accommodation prior to reaction. The measurements also show that the dynamics transition to a direct reaction for higher translational energies. Possible environmental impacts of heterogeneous reactions were probed by evaluating the change in the optical properties of laboratory-generated benzo[a]pyrene (BaP)-coated aerosols, after exposure to NO₃ and NO₂, at 532 nm and 355 nm by three aerosol analysis techniques: cavity ring-down aerosol spectroscopy (CRD-AS) at 355 nm and 532 nm, photoacoustic spectroscopy (PAS) at 532 nm, and an aerosol mass spectrometer (AMS). Heterogeneous reactions may lead to the nitration of organic-coated aerosols, which may account for atmospheric absorbance over urban areas. Developing a detailed understanding of heterogeneous reactions on atmospheric organic aerosols will help researchers to predict the fate, lifetime, and environmental impact of atmospherically important triatomics and the particles with which they collide.
Ph. D.

Cavity ring-down spectroscopy (CRDS) and cavity enhanced absorption spectroscopy (CEAS) are two well-established absorption spectroscopic techniques originally developed for gas-phase samples. Condensed-phase applications of these techniques still remain rare, complicated as they are by additional background losses induced by condensed-phase samples as well as the intracavity components in which the sample is constrained. This thesis is concerned with the development and application of optical-cavity-based techniques in the condensed phase. Polarization-dependent evanescent wave CRDS (EW-CRDS) has been used to study the molecular orientation at the solid/air and solid/liquid interfaces. An increase in average orientation angle with respect to the surface normal has been observed for both methylene blue and coumarin molecules as a function of coverage at the fused silica/air interface. An orientation-angle-dependent photobleaching of pyridin molecules at the fused silica/methanol interface have also been observed. EW-CRDS has also been used to monitor slow in situ photobleaching of thin dye films deposited on the prism surface. The photobleaching dynamics is interpreted as a combination of first- and second-order processes. A significant fraction of this thesis has been devoted to studying magnetic field effects (MFEs) on the kinetics of the radical pair (RP) reactions in solution, in an effort to understand the ability of animals to sense the geomagnetic field. Two novel optical-cavity-based techniques – broadband CEAS (BBCEAS) and CRDS have been developed for this purpose. BBCEAS uses a supercontinuum (SC) source as the cavity light source and a CCD camera as photodetector, enabling simultaneous acquisition of absorption spectrum across the whole visible region (400 – 800 nm). In CRDS, a tunable optical parametric oscillator has been used as the cavity light source. Combined with the switching of external magnetic field (SEMF) method, this technique allows the decay kinetics of the geminate RPs to be monitored, with nanosecond resolution. Both BBCEAS and CRDS provide sensitivity superior to single-pass transient absorption (TA), a technique traditionally used in the MFE studies. A series of photochemical systems have been studied by BBCEAS and CRDS, respectively, among which, the MFEs of drosophila melanogaster cryptochrome has been observed. Importantly, this is the first time an MFE has been observed in an animal cryptochrome, and provides key supporting evidence for the cryptochrome hypothesis of magnetoreception in animals. Besides the optical-cavity-based techniques, a novel fluorescence detection method of MFEs has also been demonstrated. This technique proved ultrahigh sensitivity when applicable.

Aerosols contribute the largest uncertainty to estimates of radiative forcing of the Earth’s atmosphere, which are thought to exert a net negative radiative forcing, offsetting a potentially significant but poorly constrained fraction of the positive radiative forcing associated with greenhouse gases. Aerosols perturb the Earth’s radiative balance directly by absorbing and scattering radiation and indirectly by acting as cloud condensation nuclei, altering cloud albedo and potentially cloud lifetime. One of the major factors governing the uncertainty in estimates of aerosol direct radiative forcing is the poorly constrained aerosol single scattering albedo, which is the ratio of the aerosol scattering to extinction. In this thesis, I describe a new instrument for the measurement of aerosol optical properties using photoacoustic and cavity ring-down spectroscopy. Characterisation is performed by assessing the instrument minimum sensitivity and accuracy as well as verifying the accuracy of its calibration procedure. The instrument and calibration accuracies are assessed by comparing modelled to measured optical properties of well-characterised laboratory-generated aerosol. I then examine biases in traditional, filter-based absorption measurements by comparing to photoacoustic spectrometer absorption measurements for a range of aerosol sources at multiple wavelengths. Filter-based measurements consistently overestimate absorption although the bias magnitude is strongly source-dependent. Biases are consistently lowest when an advanced correction scheme is applied, irrespective of wavelength or aerosol source. Lastly, I assess the sensitivity of the direct radiative effect of biomass burning aerosols to aerosol and cloud optical properties over the Southeast Atlantic Ocean using a combination of offline radiative transfer modelling, satellite observations and global climate model simulations. Although the direct radiative effect depends on aerosol and cloud optical properties in a non-linear way, it appears to be only weakly dependent on sub-grid variability.

Dans cette thèse, nous améliorons et utilisons le montage expérimental développé au laboratoire nommé femto/OPO-FT-CEAS. Ce montage combine une source laser femto/OPO, une cavité optique haute finesse et un interféromètre à transformée de Fourier. Il permet d'enregistrer des spectres sur un intervalle de 150 cm-1, avec un coefficient d'absorption minimal de 3x10-9 cm-1, à une résolution de 2x10-2 cm-1 et un temps d’acquisition de 2 heures. Un chemin d'absorption de 20 km a été obtenu dans une cellule de 145 cm. Différents miroirs à hauts indices de réflexion permettent d'accéder à deux gamme spectrales dans le domaine de l'infrarouge proche :6200-6700 cm-1 et 7700-8300 cm-1.Le montage femto/OPO-FT-CEAS a été utilisé afin d'enregistrer des spectres à température ambiante. La molécule OCS a été étudiée dans les gammes spectrales de 6200 à 6700 cm-1 et 7700 à 8300 cm-1. Les nouvelles données rovibrationnelles ont été intégrées au modèle global développé par le Prof. Fayt de l'université catholique de Louvain. Un échantillon de CO2 enrichi en oxygène 17 a également été étudié dans la gamme spectrale de 7700 à 8300 cm-1. Les données ont été traitées avec l'aide du Dr. Lyulin l'institut d'optique atmosphérique de Tomsk, Russie.Le montage femto/OPO-FT-CEAS a également été modifié pour enregistrer des spectres de molécules refroidies au sein d'un jet supersonique. Les molécules de N2O, C2H4 et H12C13CH en abondance isotopique naturelle ont été étudiées. Le montage permet de refroidir les molécules étudiées jusqu'à 10 K et un coefficient de 5x10-8 cm-1 a été obtenu. Ce montage a également permis d'enregistrer des spectres CEAS et CRDS de NH3 à des températures de 17 et 14 K respectivement. L'analyse des spectres aété réalisée avec l'aide des Profs. Fusina et Di Lonardo de l'Université de Bologne, Italie.Une cellule de 145 cm pouvant être refroidie à l'aide de réfrigérants liquides a également été développée en vue de remplacer une cellule à température ambiante de 77 cm utilisée dans le montage femto/OPO-FT-CEAS.Enfin, les montages FANTASIO+ et femto/OPO-FT-CEAS ont été utilisés afin afin d'enregistrer des spectres de HCOOH à température ambiante et à 10 K. Les données ont été traitées avec l'aide du Dr. Perrin de l'Université Paris-Créteil, France.
Doctorat en Sciences
info:eu-repo/semantics/nonPublished

碩士
國立臺灣大學
化學研究所
94
Cavity Ring-down Spectroscopy (CRDS) is a relatively new direct absorption technique and its applications are developed very quickly in recently years. The method is based on measurement of the decay rate of a pulse light trapped in an optical cavity which is formed by a pair of highly reflective(R>99.9%) mirrors. A plot of decay rate as a function of laser frequency gives the absorption spectrum. We used a pump-probe technique to study of nascent vibrational distribution and the quantum yield of Br2 following photodissociation of CH2Br2 and CHBr2Cl and then we can deduce two possible photodissociation mechanisms for CH2Br2 and CHBr2Cl to product Br2. Moreover, the results agree with a given theoretical calculation.

In recent years, the interest for mid infrared radiation has increased for both fundamental research and industrial applications, thanks to the development of continuous-wave room-temperature sources, such as quantum cascade lasers, which fulfill the requests for relatively high power, narrow emission and compact size. The main absorption lines of simple molecules lie in this spectral region and the study of their absorption spectra can give precise information on their concentration. Both these aspects enabled widespread applications of tunable laser absorption spectroscopy for real-time, in-situ and non-invasive gas sensing. Trace gas detection by optical spectroscopy plays a key role in applications that demand quantitative measurements of extremely small amounts of molecular gases. The enormous relevance and the complex interplay between climate change and anthropogenic influence, has focused the attention on mitigation of the greenhouse gases effects, the well-known increase in the average planetary temperature and the increase in atmospheric concentrations of climatically active gases, including CO2. In this context, the scientific and industrial debate focuses on possible methods for measuring and quantifying CO2 emissions from fossil sources, since the identification of markers to control and monitor the reduction of these sources is a necessary step to implement any mitigation politics. In this respect, radiocarbon method represents the most promising approach to validate the estimations provided by single nations or companies. Indeed, radiocarbon is a natural clock, with a lifetime of about 5,700 years, and the measurement of its concentration is an optimal approach to distinguish "young" samples from very old ones, like fossil fuels, completely depleted in radiocarbon. However, ultra-high detection sensitivity is required to quantify radiocarbon due to its extremely low natural abundance being about one part per trillion (10-12) in the biosphere. Thanks to the combination of continuous wave-cavity ring down spectroscopy (CW-CRDS) and strong absorption from fundamental ro-vibrational molecular transitions in the midinfrared, we can overcome the detection limit imposed by the small amount of molecular gases. Nevertheless, state of-the-art conventional CW-CRD spectrometers in the mid IR cannot reach the minimum detectable absorption level required to detect 14CO2, mainly because of the empty-cavity decay rate fluctuations. To overcome this limitation, about ten years ago a novel high-resolution and high-sensitivity spectroscopic technique was proposed: Saturated-Absorption Cavity Ringdown (SCAR) spectroscopy. This technique has shown to improve by more than one order of magnitude the limits of conventional linear-absorption CRDS, thanks to a sample absorption measurement which is independent from the other cavity losses during the same cavity decay event. Indeed, SCAR, benefiting from both CW-CRDS and saturation spectroscopy, overcomes the limits of linear CRD by measuring in each and every single decay event both the "empty" and the "full" cavity contribution. Thanks to the achieved sensitivity, detection of rare molecular species, such as radiocarbon dioxide, was demonstrated. With this work, we describe disruptive applications of this technique, by accurately measuring radiocarbon dioxide concentrations. In particular, these three application areas were targeted: the biogenic fraction in biofuel and bioplastics; parts of concrete walls from nuclear power plants for decommissioning purposes; dating of archaeological samples from Sumer settlements. Specific, customized sample purification processes as well as measurements schemes have been devised.

Cavity ring-down spectroscopy has been used over the last twenty years as a highly sensitive absorption spectroscopic technique to measure light attenuation in gases, liquids, and solid samples. An optical cavity is used as a multi-pass cell, and the decay time of the light intensity in the cavity is measured, thereby rendering the techniques insensitive to light intensity fluctuations. Optical waveguides are used to build the optical cavities presented in this work. The geometries of such waveguides permit the use of very small liquid sample volumes while retaining the advantages of cavity ring-down spectroscopy. In this thesis cavity ring-down measurements are conducted, both, in the time domain and by measuring phase-shifts of sinusoidally modulated light, and the two methods are theoretically connected using a simple mathematical model, which is then experimentally confirmed. A new laser driver, that is compatible with high powered diode lasers, has to be designed to be able to switch from time domain to frequency domain measurements. A sample path length enhancement within the optical cavity is explored with the use of liquid core waveguides. The setup was optimised with respect to the matrix liquid, the geometrical matching of waveguide geometries, and the shape of liquid core waveguide ends. Additionally, a new technique of producing concave lenses at fibre ends has been developed and the output of a general fibre lens is simulated. Finally, liquid core waveguides are incorporated into a fibre-loop ring-down spectroscopy setup to measure the attenuation of two model dyes in a sample volume of <1 µL. The setup is characterized by measuring concentrations of Allura Red AC and Congo Red from 1 µM to a limit of detection of 5 nM. The performance of the setup is compared to other absorption techniques measuring liquid samples.
Thesis (Ph.D, Chemistry) -- Queen's University, 2013-04-23 14:08:16.33

碩士
國立臺灣大學
化學研究所
93
Cavity ring-down Spectroscopy (CRDS) is a relatively new direct absorption technique and its applications are developed very quickly in recently years. The method is based on measurement of the decay rate of a pulse light trapped in an optical cavity which is formed by a pair of highly reflective(R>99.9%) mirrors. A plot of decay rate as a function of laser frequency gives the absorption spectrum. As for photodissociation studies of CF2Br2, the major dissociation channels are found to be CF2Br2 → CF2Br + Br ΔH=274 kJ/mol CF2Br2 → CF2 + Br2 ΔH=231 kJ/mol We used a cavity ring-down spectroscopy (CRDS) to study of nascent Br2 following photodissociation of CF2Br2. The quantum yield of Br2 is found to be 0.038±0.009 following photodissociation of CF2Br2 at 248nm. According to the absorption spectrum, the nascent vibrational distribution was obtained. A comparison with the CHBr3 case reveals that nascent vibrational distribution leads to vibrationally cool. The excited parent molecules (CF2Br2) may transfer into highly vibrational levels of their electronic ground state via internal conversion. The results agree with a given theoretical calculation.

碩士
國立臺灣大學
化學研究所
101
Evanescent wave cavity ring-down absorption spectroscopy (EW-CRDS) is employed to study the interaction between deoxyribonucleic acids (DNA) by functionalized gold nanoparticles (Au NPs). EW-CRDS is a surface sensitive technique based on the measurement of the decay rate of a pulsed laser light trapped in an optical cavity. The light undergoes total internal reflection (TIR) at an interface of a prism within the cavity and creates an evanescent field at the surface that is sensitive to small absorption changes and is particularly useful for investigating interfacial processes. EW-CRDS offers a significantly higher sensitivity than conventional absorption spectroscopy with a rather simple and straightforward experimental set-up. The high sensitivity results mainly from its independence of fluctuations of the light source and the extremely long effective path length realized in optical cavities. By applying this ultra-sensitive EW-CRDS to the observation of DNA, we were able to study the binding kinetics of DNA and obtain the association equilibrium constants (Ka) and the free energies (ΔG). Binding conditions such as changes in the salt concentration, buffer pH and temperature are systematically examined. This basic study gives further insight in the design of DNA detection for DNA mutation diseases.

碩士
國立交通大學
應用化學系碩博士班
100
We employed a cavity ringdown spectrometer with a tunable infrared OPO/OPA laser with a bandwidth of 0.02 cm-1 to record the absorption spectra of methylperoxy radicals (CH3OO) in the range 2930-3050 cm-1. Methylperoxy radicals were produced by irradiating a flowing mixture of CH3I and O2 with emission at 248 nm from a KrF excimer laser or a flowing mixture of CH3C(O)CH3 and O2 with emission at 193 nm from an ArF excimer laser. Two absorption bands with origins at 2953.4 cm-1 and 3020.7 cm-1 were observed; they are assigned to ν2 (symmetric CH3 stretching) and ν9 (antisymmetric CH2 stretching) modes of CH3OO, respectively. We analyzed the rotational structures of the ν2 and ν9 bands by simply treating CH3OO as a prolate symmetric top, and determined the rotational constants both in the ground state and in the vibrationally excited state. We predicted vibrational wavenumbers and rotational parameters for the upper and lower vibrational states, and the mixing ratio among a-, b-, c-types of bands of CH3OO with the B3LYP/aug-cc-pVTZ density-functional theory. The rotational contours for the ν1, ν2 and ν9 bands of CH3OO were simulated with the SpecView software. For the ν2 band, the simulation agrees satisfactorily with the experimental observations except for the intense peaks with regular spacing about 2.4 cm-1 in the range 2940-2950 cm-1. For the ν9 band, the simulation result is consistent with the experimental observations in the region 3000-3020 cm-1 but not in the region 3020-3050 cm-1. The discrepancy might be due to the interference from the ν1 band. That ν1 band is unobserved is likely due to its relatively small intensity. We temporarily assigned the ν1 band to be at 3031.7 cm-1 by matching the simulated spectra with the peaks which do not correspond to the ν9 band.

碩士
國立臺灣大學
化學研究所
99
Abstract SDS (Sodium dodecyl sulfate, SDS) is an anionic surfactant that commonly used in many cleaners and hygiene products. At low surfactant concentration in aqueous solution, surfactant molecules exist the form of monomers. At surfactant concentrations above the critical micelle concentration(CMC), surfactant molecules in solution will spontaneously come together to form micelles (micelle), the formation of the micelle is usually detected by the changes in the physical properties of the solution, such as surface tension, conductivity or turbidity. Evanescent wave cavity ring-down spectroscopy (EW-CRDS) is based on the measurement of the decay rate of the light which goes back and forth (ring-down) in an optical cavity formed by two mirrors with extremely high reflectivity. There are two types of silanol groups at the silica/water interface with different pKa values, 4.9 and 8.5. With pKa = 4.9, the proton of the silanol group can easily dissociate, thus causing the interface to be negative. In our experiment, we choose crystal violet as molecular probes to determine surface critical micelle concentration (SCMC) of SDS. Similar, by the addition of NaCl electrolytes and changing the length of the chain of a hydrocarbon surfactant, we can obtain different surface CMC from the pure water.

博士
國立臺灣大學
化學研究所
92
Part I In this thesis, it will be separated into two individual parts: part I and part II. Each part has two chapters. In the chapter 1 of part I, some basic background of spectroscopy and Fourier transform infrared method is illustrated. And in the chapter 2 of part I, the fine state-resolved rotational and vibrational energy transfer of CH B2Σ- (v’=1, N) by collisions with Ar, CO, and N2O is illustrated. It is the first time to observe the rotational energy transfer and vibrational energy transfer processes of a specific fine state for B 2Σ- (v’=1) of CH radical. We use pump-probe technique to determine RET and VET rate constants of CH B (v’ = 1, 0≦ N ≦ 6) with collisions of Ar, CO, and N2O. The RET is anticipated to be larger than VET for each collider. The determined RET rate constants range from 10-11 to 10-10 cm3 molecule-1 s-1, while the determined VET rate constants range from 10-12 to 10-11 cm3 molecule-1 s-1. The relative values of RET and VET rate constants are consistent with the results founded by Cooper and Whitehead. The findings of multi-quantum changing within single collision suggest that the collisions possibly dominated by the long-range attractive force. The k’VET shows no rotational quantum number dependence for these three quenching gases. This conclusion is the same as the results reported previously by Crosley et al. and Whitehead et al. The kVET of N2O is three times larger than that of CO and nine times larger than that of Ar, respectively. This result is related to polyatomic effect, permanent dipole moment, and inefficient vibration-translation transfer. The number of internal degrees of freedom of N2O is larger than that of CO and Ar, therefore N2O can remove more energy than CO and Ar within single collision. In other words, N2O is more efficient than CO and Ar. Polyatomic effect and permanent dipole moment play a role in vibration and rotational energy transfer process. Part II In the chapter 1 of part II, the basic working principle of cavity ring-down absorption spectroscopy (CRDAS) is introduced. In the first section in the chapter 2 of part II, the total continuous absorption which includes A – X, B – X, and C – X transition of pure diatomic bromine is obtained by using CRDAS. In the second section, the primary photodissociation channels of CHBr3 and CH2Br2 which is ignored in the past studies have been investigated. CHBr3 + hν -->�� CHBr + Br2 CH2Br2 + hν -->�� CH2 + Br2 The quantum yields of Br2 are found to be 0.23±0.05 and 0.26±0.07 following photodissociation of CHBr3 and CH2Br2 at 248nm, respectively. According to the absorption spectrum, the nascent vibrational distribution can be obtained. The bromine molecules resulted from photodissociation of CHBr3 or CH2Br2 at 248 nm are both lying at a vibrationally hot distribution. The excited parent molecules (CHBr3 and CH2Br2) may couple into highly vibrational levels of their electronic ground state via internal conversion, which could lead to vibrationally hot Br2 photofragment.