Thèses : « Ring down spectroscopy »

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Bitter, Mario. « Cavity ring down spectroscopy for atmospheric applications ». Thesis, University of Cambridge, 2004. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.616079.

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Castillo, Genevieve Montero. « Biosensor using evanescent wave cavity ring-down spectroscopy (EWCRDS) ». abstract and full text PDF (free order & ; download UNR users only), 2007. http://0-gateway.proquest.com.innopac.library.unr.edu/openurl?url_ver=Z39.88-2004&rft_val_fmt=info:ofi/fmt:kev:mtx:dissertation&res_dat=xri:pqdiss&rft_dat=xri:pqdiss:1447616.

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Cengiz, Betul. « Fiber Loop Ring Down Spectroscopy For Trace Chemical Detection ». Master's thesis, METU, 2013. http://etd.lib.metu.edu.tr/upload/12615626/index.pdf.

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Fiber loop ring down (FLRD) spectroscopy is a sensitive spectroscopic technique that is based on absorption and it is convenient for trace chemical detection. Different FLRD systems are being improved in order to increase their sensitivity. In FLRD spectroscopy, detection of a sample is done by measuring of a leaking light at each trip within an optical cavity. Intensity of leaking light has an exponential decay where it is reduced by absorption of sample and scattering of light. In this project, two FLRD set-ups at 1535 nm and 808 nm were designed. In both set-ups, optical fiber and optical fiber couplers are used to form a cavity. At 1535 nm, a FLRD set-up is constructed by utilizing a pulsed laser and used for characterization of thin films, various pure liquids and fluorescein solutions. Two different sensor regions are designed with free space collimators and ferrules for the measurement of thin films and liquids, respectively. The future endeavor of the set-up is improvement for reliability and reproducibility of the system. For visible and NIR regions, a fiber coupled laser with four colors as 642 nm, 785 nm, 808 nm and 852 nm laser is used to design of a FLRD set-up. 808 nm laser is selected to build a prototype of the FLRD system. The construction of a closed loop FLRD set-up is completed and the system is characterized. Ultimate aim in our project is to be able to do trace detection at visible and NIR regions where the chemical sensitivity is higher.

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Fiadzomor, Phyllis Aku Yayra. « Trace detection of water vapour by cavity ring-down spectroscopy ». Thesis, University of Bristol, 2008. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.492638.

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A continuous wave cavity ring-down (CRD) spectrometer has been developed for the measurement of trace levels of water vapour by absorption spectroscopy at wavelengths m make cavity ring-down spectroscopy potentially more useful than current techniques for measurement of trace water in process gases and vacuum environments of semiconductor manufacture where water vapour contamination has a detrimental effect on the final product.

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Mason, Bernard James. « Aerosol cavity ring down spectroscopy : from ensemble to single particle measurements ». Thesis, University of Bristol, 2014. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.658637.

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Aerosol particles are prevalent in the atmosphere and impact the Earth's energy balance through scattering and absorption of incoming and outgoing radiation. Such particles represent one of the largest uncertainties when trying to characterise the anthropogenic causes in the Earth's changing radiation balance. This thesis describes the development of laboratory based techniques for measuring aerosol optical and microphysical properties that are atmospherically relevant. A single particle trapping technique that uses a Bessel-beam propagating counter to a' gas flow (Bessel-beam/gas-flow) is presented. The changing radius of the trapping particle is determined from the collected elastically scattered light. The fluctuating position of a particle trapped along the Bessel beam length is shown to be directly related to the particle radiation pressure efficiency and thus to its radius and refractive index counter to what is expected from , liquid phase optical chromatography measurements. It is shown that ensemble aerosol particle fractionation using a Bessel-beam/gas-flow instrument is not possible. An aerosol ensemble cavity ring down spectrometer (AE-CRDS) was used to determine the refractive index of hygroscopic sodium nitrate aerosols at different relative humidities, A comparison is made between the refractive index retrieved using AE-CRDS and the refractive index retrieved using a single particle, optical tweezers instrument. The accuracy of the optical tweezers refractive index measurement is found to be significantly higher due to the poorly defined size distribution of the aerosol ensemble in the cavity ring down technique. The development of the single particle cavity ring down spectroscopy (SP-CRDS) technique for highly accurate measurements of aerosol extinction efficiencies is presented. The SP-CRDS instrument uses a Bessel-beam/gas-flow optical trap to control the position of a particle within a cavity ring down spectrometer. A new method of accurately obtaining the real part of the refractive index using this technique is described. Measured extinction efficiencies are compared to Mie simulated extinction efficiencies to obtain the refractive index of single component aerosol particles to an accuracy of better than ± 0.1%.

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Fawcett, Beth. « Diode laser cavity ring down spectroscopy for the measurement of trace gases ». Thesis, University of Bristol, 2003. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.274627.

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Kim, Jin. « Use of cavity ring-down spectroscopy for the retrieval of aerosol refractive indices ». Thesis, University of Bristol, 2011. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.541642.

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Rabeau, James Robert. « The cavity ring-down spectroscopy of C₂ in a diamond forming microwave plasma ». Thesis, Heriot-Watt University, 2003. http://hdl.handle.net/10399/1148.

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Burkart, Johannes. « Optical feedback frequency-stabilized cavity ring-down spectroscopy - Highly coherent near-infrared laser sources and metrological applications in molecular absorption spectroscopy ». Thesis, Université Grenoble Alpes (ComUE), 2015. http://www.theses.fr/2015GREAY045/document.

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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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MARTINS, JULIANNA MARIA DE ALMEIDA. « CAVITY RING-DOWN SPECTROSCOPY AS A TOOL FOR THE DETERMINATION OF CARBON ISOTOPE DISTRIBUTION ». PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO, 2012. http://www.maxwell.vrac.puc-rio.br/Busca_etds.php?strSecao=resultado&nrSeq=20983@1.

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PONTIFÍCIA UNIVERSIDADE CATÓLICA DO RIO DE JANEIRO
CONSELHO NACIONAL DE DESENVOLVIMENTO CIENTÍFICO E TECNOLÓGICO
A análise isotópica vem crescendo a cada ano devido à sua grande área de atuação nas diversas áreas da ciência. Existem diversas técnicas utilizadas para realizar a determinação das concentrações naturais dos isótopos e suas variações, sendo que a mais utilizada é a espectrometria de massa de razões isotópicas (EMRI). Uma técnica analítica que vem ganhando espaço no mercado é a espectroscopia de cavidade ressonante do tipo ring-down (ECRRD) (Cavity Ring-Down Spectroscopy - CRDS), que é uma técnica baseada em laser. Ao contrário dos espectrômetros de massa, estes analisadores exigem pouco ou nenhum tratamento da amostra, diminuindo com isso o tempo de análise. O presente trabalho tem como objetivo obter a assinatura isotópica 13C/12C em amostra sólidas e líquidas, empregando um analisador a laser. Foi desenvolvido e implementado um método de análise isotópica empregando um analisador de carbono orgânico total acoplado a um espectrômetro de cavidade ressonante do tipo ring-down (iTOC-CRDS). Os resultados obtidos foram comparados com os obtidos através de um EMRI. O desempenho do método foi avaliado através dos parâmetros de linearidade; exatidão, pela utilização de materiais de referência certificados; precisão, pela repetitividade e reprodutibilidade; além dos cálculos das incertezas associadas. Foram analisadas amostras de açúcar, biomassas, bio-óleo, biocombustível, metanol e gasolina.
The use of isotopic analyses grows each year, due to large area of expertise in several science areas. Several techniques are used to perform the determination of natural isotope concentrations and their variations, with isotopic ratio mass spectroscopy (IRMS) being the most widely used. An analytical technique that is gaining market space is the cavity ring-down spectroscopy. Unlike mass spectrometers, these analyzers require little or no sample treatment, thereby reducing the analysis time. The present study aimed to obtain the 13C/12C isotopic signature in solid and liquid samples using a laser analyzer. An isotopic analysis method using a total organic carbon analyzer coupled to a cavity ring-down spectrometer (iTOC-CRDS) was developed and implemented. The results were compared with those obtained by IRMS. The method performance was evaluated by the parameters of linearity; accuracy, using standard reference materials; precision, using parameters of repeatability and reproducibility and by calculating the associated uncertainties. The analyzed samples were sugar, biomass, bio-oil, biofuel, methanol and gasoline.

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Bîrzǎ, Petre A. « Development of a cw-cavity ring down spectrometer and electronic spectroscopy of transient species / ». Basel : [s.n.], 2004. http://edoc.unibas.ch/diss/DissB_6934.

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Zhu, Xijing. « Investigation of Aerosol Optical and Chemical Properties Using Humidity Controlled Cavity Ring-Down Spectroscopy ». PDXScholar, 2017. https://pdxscholar.library.pdx.edu/open_access_etds/4032.

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Scientists have been observing a change in the climate since the beginning of the 20th century that cannot be attributed to any of the natural influences of the past. Natural and anthropogenic substances and processes perturb the Earth's energy budget, contributing to climate change. In particular, aerosols (particles suspended in air) have long been recognized to be important in processes throughout the atmosphere that affect climate. They directly influence the radiative balance of the Earth's atmosphere, affect cloud formation and properties, and are also key air pollutants that contribute to a variety of respiratory and cardiovascular diseases. Despite their importance, aerosol particles are less well-characterized than greenhouse gases with respect to their sources, temporal and spatial concentration distribution, and physical and chemical properties. This uncertainty is mainly caused by the variable and insufficiently understood sources, formation and transformation processes, and complex composition of atmospheric particles. Instruments that can precisely and accurately measure and characterize the aerosol physical and chemical properties are in great demand. Atmospheric relative humidity (RH) has a crucial impact on the particles' optical properties; the RH dependence of the particle extinction coefficient is an important parameter for radiative forcing and thus climate change modeling. In this work a Humidity-Controlled Cavity Ring-Down (HC-CRD) aerosol optical instrument is described and its ability to measure RH dependent extinction coefficients and related hygroscopicity parameters is characterized. The HC-CRD is capable of simultaneously measuring the aerosol extinction coefficient at three wavelengths (λ = 355, 532, and 1064 nm) and three different RHs (typically 20%, 50%, and 80%). A range of chemicals and their mixtures were used to produce laboratory generated aerosols. Three mixture systems include one inorganic salts mixture system consisting of (NH4)2SO4, NH4HSO4, Na2SO4, NaHSO4 serve as surrogates of the ionic salts found in the atmosphere. Two organic mixture systems were investigated: mixtures of NaCl, D-glucose, sucrose, and glycine are benchmarks for compounds emitted from biomass burning. Finally, mixtures of (NH4)2SO4 (ammonium sulfate, AS) with a series of dicarboxylic acids including malonic acid, adipic acid, and azelaic acid are used as benchmarks to mimic urban pollutants. The extinction coefficients were obtained as a function of RH from the HC-CRD measurements, from which optical growth factors f(RH) and γ(RH) values can be determined to examine their dependence on chemical composition. A volume mixing rule was used to calculate the effective refractive index of the binary substrate mixtures, since both size and composition change during water uptake. The SDA/FMC algorithm developed by O'Neill, et al. 2005 is used to extract the van de Hulst phase shift parameter (Ρeff) from three-wavelength measurements of extinction. The fine mode fraction of extinction (η) and fine mode effective radius (Reff) of laboratory generated aerosol particles can be then determined. An iterative algorithm was developed to retrieve the change in refractive index of particles as function of RH. The calculated Reff of aerosols at different RHs were used to obtain the physical size growth factor (gf), and κ(RH). The size changes as a function of water uptake describe the dependence of aerosol optical properties on chemical composition. This work demonstrates the capability of conducting aerosol optical measurements using HC-CRD to determine the RH dependence of aerosol optical properties. The HC-CRD measurements combined with the SDA/FMC method to retrieve aerosol size for laboratory generated aerosols establish the connection between the optical properties and the aerosol particles' chemical compositions. It also underlines the importance and need for future investigation on the hygroscopic properties of atmospheric aerosols. This work is successfully developed a method that enables using the aerosols optical measurements to predict the compositions; it will greatly contribute to the atmospheric aerosol measurement and global climate modelling.

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Robichaud, David Joseph Blake Geoffrey A. Okumura Mitchio Chen Pin. « High-resolution study of the O2 A-band using frequency stabilized cavity ring-down spectroscopy / ». Diss., Pasadena, Calif. : Caltech, 2008. http://resolver.caltech.edu/CaltechETD:etd-05212008-152946.

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Courtois, Jérémie. « Développements de systèmes multipassages pour application à la spectroscopie d'absorption : Cavity Ring Down Spectroscopy multimode et cellules à passages multiples ». Phd thesis, Université Paris Sud - Paris XI, 2009. http://tel.archives-ouvertes.fr/tel-00458101.

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La spectroscopie d'absorption par mesure du temps de vie des photons piégés dans une cavité optique haute-finesse, ou Cavity Ring Down Spectroscopy (CRDS), compte parmi les outils de diagnostic optique les plus sensibles. L'excitation « mode matchée » d'un laser continu rapidement et continûment balayé (~4 THz.s-1 durant ~2 ms), i.e. la cw-CRDS monomode rapide, garantit à la technique ses meilleures performances en termes de limites de détectivité avec, en contrepartie, des points de mesures séparés de l'Intervalle Spectral Libre du résonateur (ISL=c/2L) : le dosage d'environnements basse pression requiert de longues cavités. Cette étude originale propose de mettre à profit la structure transverse du résonateur afin de rendre possible la miniaturisation du dispositif de cw-CRDS rapide. L'excitation multimode d'une cavité fractionnellement dégénérée (dite de taille « magique »), ici présentée, permet de bénéficier d'un gain d'échantillonnage spectral qui vaut l'ordre réentrant N employé. Nous développons deux schémas d'injection multimode : l'injection multimode axiale et l'injection multimode réentrante, dite dans ce dernier cas hors de l'axe optique, de telles cavités et nous en étudions les principales différences. Une étude détaillée du champ intracavité existant aux N résonances constitutives de l'ISL est proposée afin de rendre compte des limites de détectivités associées à ces deux schémas d'injection multimode sensiblement distincts. Une seconde partie de ce travail de thèse est dédiée à caractériser de façon approfondie l'observation des profils spatiaux intracavités formés en injection hors axe lorsque la cavité souffre d'un faible astigmatisme (ΔR/R~2 %) : on parle de profil de Lissajous. Cette étude rend compte des mécanismes fondamentaux, telle la coïncidence particulière de modes particuliers par dispersion modale, qui aboutissent en un intervalle millimétrique de dégénérescence. Celui-ci est le siège d'une succession de profils transverses de Lissajous symétriques les uns des autres de part et d'autre d'une taille particulière de cavité : nous en précisons les causes. Le résiduel astigmatisme ainsi mis en évidence et mesuré permet, en outre, d'expliquer la disparition des oscillations Doppler normalement présentent en début de décroissance ring down dans ce type d'injection dynamique. De façon connexe, nous développons plusieurs types de cellules multipassages non-résonantes comme alternative à la CRDS pour le dosage d'environnements hostiles.

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Courtois, Jérémie. « Développement de systèmes multipassages pour application à la spectroscopie d'absorption : cavity ring down spectroscopy multimode et cellule à passages multiples ». Paris 11, 2009. http://www.theses.fr/2009PA112286.

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L’utilisation de systèmes multipassages est un des moyens pour augmenter la sensibilité du dosage optique d’espèces gazeuses à l’état de trace ou présentant de faibles transitions optiques. Il s’agit, littéralement, de piéger la lumière entre deux (ou plusieurs) miroirs afin de rendre efficace l’interaction laser-matière. En l’occurrence, nous cherchons un outil de spectroscopie d’absorption suffisamment rapide et sensible pour la métrologie transitoire de l’oxygène moléculaire (O2) en écoulement hypersonique (soufflerie F4). Ce travail de thèse présente les développements réalisés sur deux systèmes multipassages : la Cavity Ring Down Spectroscopy (CRDS) et les cellules multipassages. Relativement à la technique CRDS, le schéma rapide et continu mis en œuvre à l’Onera présente un échantillonnage spectral insuffisant pour garantir la métrologie de milieux basse pression (régime Doppler) par de petites cavités. Cette étude porte sur la mise à profit de la structure transverse d’une cavité fractionnellement dégénérée. Nous mettons par ailleurs en évidence, puis caractérisons, le comportement d’une cavité optique haute finesse excitée hors de son axe optique et qui possède, de façon inéluctable, un infime astigmatisme. Comme alternative au dosage de l’O2 en milieu « inhospitalier » (F4), nous présentons également les développements accomplis sur les cellules multipassages non-résonantes
Multipassages systems constitute one of the ways to increase the sensitivity of optical probing of gaseous species status trace or with low optical transitions. It involves of trapping, literally, the light between two (or more) mirrors so as to make efficient laser-matter interaction. In this case, we are looking for an absorption spectroscopic tool sufficiently rapid and sensitive for transitional metrology of molecular oxygen (O2) in the F4 hypersonic flow facility. This thesis work presents developments carried out on two multipass systems: Cavity Ring-Down Spectroscopy (CRDS) and multipass cells. Relative to the CRDS technique, the rapid and continuous scheme implemented at Onera presents an insufficient spectral sampling to ensure workplaces metrology low-pressure (Doppler scheme) by small cavities. This study examines the transverse structure of a fractionnellement degenerate cavity. We highlight also, and then characterize, the behavior of a high finesse cavity which if off-axis excited and which suffers, naturally, a weak astigmatism. As an alternative to the determination of the O2 in the workplace "inhospitable" (F4), we also present developments on non resonant multipass cells

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Amick, Cecilia Lynn. « Instrument development for exploring the influence of interfacial chemistry on aerosol growth, aging, and partitioning of gases ». Diss., Virginia Tech, 2019. http://hdl.handle.net/10919/103541.

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Investigation of aerosol chemistry and growth under atmospheric conditions in a novel rotating aerosol suspension chamber with cavity ring-down spectroscopy provided key insight into the effect of pollutants and other vapors on the overall atmospheric lifetime of particulate matter. The Atmospheric Cloud Simulation Instrument (ACSI) creates a well-defined and controllable atmosphere of suspended particles, analyte gases, and background gas molecules, which remains stable up to several days. Preliminary studies have shown that monodisperse polystyrene latex (dp = 0.994 µm) and polydisperse ammonium sulfate (CMD dp = 100 nm) particles remain suspended for at least 22 hours while the chamber rotates at 2 RPM. Further investigation into the aerosol dynamics showed the coagulation efficiency of high concentration particle suspensions (>10^6 particles/cm3) depends on particle phase state and composition. The coagulation efficiency decreased with increased humidity in the model atmosphere and with increased ion concentrations in the aerosols. The decrease in efficiency is attributed to repulsive forces from like-charges on the particle surfaces. In addition to humidity, the spectroscopy integrated into the main chamber monitors the real-time response to a perturbation in the model atmosphere, such as the introduction of a gas-phase reactant. Cavity ring-down spectroscopy, performed in situ along the center axis, records mid-infrared spectra (1010 cm-1 to 860 cm-1) to identify gas species evolved from gas-particle heterogeneous chemistry. In accord with previous studies, my results show that a known reaction between monomethyl amine and ammonia occurs readily on suspended ammonium sulfate particles in >50% RH and the extent of the reaction depends on the humidity of the model atmosphere. Acidic ammonium bisulfate aerosols also produced a detectable amount of ammonia upon exposure to monomethyl amine in a model atmosphere with >50% RH. Overall, the new ACSI approach to atmospheric science provides the opportunity to study the influence of interfacial chemistry on particle growth, aging, and re-admission of gas-phase compounds.
Doctor of Philosophy
"Molecules don't have a passport." - Carl Sagan. Gas molecules and particles emitted into the atmosphere in one area can travel thousands of kilometers over the course of hours to days, even weeks for some compounds. The gas-solid interactions that occur over the lifetime of particulate matter are largely unknown. I focused my doctorate on bridging the knowledge gap between traditional environmental monitoring research and highly controlled laboratory experiments. To do so, I designed a new instrument capable of creating stable model atmospheres that more accurately simulate the gas-particle interactions in Earth's atmosphere than previous environmental chambers. The Atmospheric Cloud Simulation Instrument design included a rotating chamber to increase the duration of stable particle suspensions in a laboratory and a multi-pass infrared spectrometer to monitor gas-phase reactions in situ. I explored the effect of humidity and particle composition on particle-particle coagulation and gas-particle reactions. For example, liquid aerosols at humidities higher than 35% RH do no coagulate as fast as a solid particle with the same composition in <35% RH. Similarly, the same liquid aerosols produced more gaseous product during a heterogeneous reaction with a 'pollutant' gas than solid particles. Overall, the ACSI will be an important tool for future experiments exploring individual aspects of complex atmospheric processes.

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Debecker, Isabelle. « Développement de dispositifs de Cavity Ring Down Spectroscopy rapide pour la caractérisation d'écoulements transitoires et inhomogènes ». Paris 11, 2006. http://www.theses.fr/2006PA112088.

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Le développement de nouveaux outils de diagnostic optique est nécessaire pour analyser de manière plus rapide et plus sensible les écoulements réactifs transitoires. La Cavity Ring Down Spectroscopy en régime continu (cw-CRDS) présente un fort potentiel pour répondre à ces attentes. Les dispositifs actuels sont toutefois assez complexes et offrent des cadences d'acquisition limitées. L'objectif de cette étude est de développer une cw-CRDS plus rapide et plus simple, adaptée à la métrologie des écoulements transitoires produits dans des installations de type soufflerie ou chambre de combustion. Le schéma de cw-CRDS proposé repose sur l'injection de la cavité au cours d'un balayage rapide et continu de la fréquence du laser, sans extinction optique et sans moyenne des signaux. Après avoir modélisé les événements de Ring Down obtenus par passage en résonance du laser, la technique est validée expérimentalement en enregistrant des profils de raie d'absorption du dioxygène autour de 766. 7 nm en moins de 2 ms. Les résultats de l'implantation de la CRDS rapide en soufflerie hypersonique sont également présentés. Ensuite, nous étudions une nouvelle approche destinée à augmenter la résolution spectrale du dispositif. La méthode repose sur l'utilisation d'un balayage simultané du laser et de la cavité. Les gains en résolution accessibles sont évalués théoriquement puis expérimentalement. Finalement, nous explorons la faisabilité de mesures locales par cw-CRDS rapide, en vue de la caractérisation de milieux inhomogènes
The development of new optical sensing tools is needed to perform faster and more sensitive analysis of transient reactive flows. Continuous wave Cavity Ring Down Spectroscopy (cw-CRDS) offers a great potential to fulfil these requirements. The current devices exhibit high sensitivity, in spite of a relative complexity and limited acquisition rates. The aim of this study is thus to develop a faster and simpler cw-CRDS scheme, in order to use the technique for the metrology of transient flows produced in research or industrial installations (wind tunnels, combustion systems, exhaust ducts). The cw-CRDS design which is proposed is based on the cavity injection during a rapid and continuous tuning of the laser frequency, without any optical switch or averaging procedures of the signals. After simulating the Ring Down events that are obtained during a pass of the laser through resonance, our strategy is validated by recording experimental O2 absorption line profiles near 766. 7 nm. A 1. 1 10-9-cm-1-Hz-1/2 detection limit is obtained. The results of the integration of fast cw-CRDS in hypersonic wind tunnels are also shown. Then, we present a new approach to increase the spectral resolution of fast cw-CRDS and obtain well-defined absorption line profiles at low pressure. The method employs a simultaneous sweep of the laser and the cavity. The obtainable gains are evaluated theoretically and experimentally. Finally, we explore the potential application of fast cw-CRDS to make local measurements and characterize inhomogeneous media

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Khoroshev, Dmitriy. « Electronic spectroscopy of carbon chain radicals using cw cavity ring down in conjunction with mass detection / ». Basel : [s.n.], 2005. http://edoc.unibas.ch/diss/DissB_7132.

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NAKAEMA, WALTER M. « Espectroscopia de cavidade ressonante tipo ring-down supercontinuum resolvida no tempo para deteccao de multicomponentes gasosos ». reponame:Repositório Institucional do IPEN, 2010. http://repositorio.ipen.br:8080/xmlui/handle/123456789/9590.

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Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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Vasilchenko, Semen. « Development of an ultrasensitive cavity ring down spectrometer in the 2.10-2.35 µm region : application to water vapor and carbon dioxide ». Thesis, Université Grenoble Alpes (ComUE), 2017. http://www.theses.fr/2017GREAY037/document.

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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

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Salffner, Katharina. « Entwicklung eines breitbandigen Cavity-Ring-Down-Spektrometers unter Verwendung nahinfraroter, inkohärenter Strahlung ». Phd thesis, Universität Potsdam, 2013. http://opus.kobv.de/ubp/volltexte/2013/6895/.

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In der vorliegenden Arbeit werden verschiedene Spektrometer für die Analyse von Gasen bzw. Gasgemischen vorgestellt und deren Design, Aufbau, Charakterisierung und Optimierung beschrieben. Das Resultat der Optimierung und Weiterentwicklungen ist ein spektral breitbandiges Cavity-Ring-Down-Spektrometer (CRD-Spektrometer). Ausgangspunkt der hier vorgestellten Arbeit ist ein Spektrometer auf Basis klassischer Absorptionsspektroskopie in einer Multireflexionszelle. Für dieses Spektrometer wurde als Strahlquelle ein Superkontinuumlaser verwendet. Der Vorteil dieses Spektrometers liegt in seiner Kompaktheit. Mit diesem Spektrometer wurden Absorptionsspektren von mehreren Reingasen und einem Gasgemisch über einen Wellenlängenbereich von 1500 nm – 1700 nm aufgenommen. Der qualitative Vergleich mit zu erwartenden Spektren, welche auf der HITRAN-Datenbank basieren, zeigte eine gute Übereinstimmung. Die quantitative Interpretierbarkeit der Daten war jedoch stark eingeschränkt aufgrund des hohen zufälligen und systematischen Fehlers der Messungen. Als Konsequenz aus der als nicht zufriedenstellend bewerteten quantitativen Interpretierbarkeit der Daten wurde eine alternative Messmethode gesucht, welche eine höhere Sensitivität und Genauigkeit ermöglicht. Die Wahl fiel auf die Cavity-Ring-Down-Spektroskopie, eine resonatorgestützte Variante der Absorptionsspektroskopie. Wesentliche Vorteile dieser Technik sind a) die Unabhängigkeit von Leistungsschwankungen der Strahlquelle, b) ein effektiver Absorptionsweg von bis zu mehreren Kilometern, welcher sich unmittelbar auf die Sensitivität der Messungen auswirkt, c) die Ermittlung absoluter Absorberkonzentrationen, ohne die Notwendigkeit einer Kalibrierung oder den Vergleich mit einer Referenzzelle und d) die Vernachlässigbarkeit von Absorptionen außerhalb des Resonators. Als notwendiger Zwischenschritt auf dem Weg zu einem breitbandigen CRD-Spektrometer wurde zunächst ein monochromatisches CRD-Spektrometer designt, aufgebaut und charakterisiert. Für die effektive Einkopplung von Strahlungsenergie in einen Resonator ist die Anpassung der Strahlparameter an die Mode des Resonators notwendig. Voraussetzung dieser Anpassung ist die Kenntnis der Strahlparameter, welche experimentell ermittelt wurden. Im Laufe des Aufbaus des Spektrometers ergab sich, dass trotz der Modenanpassung die Einkopplung der Strahlungsenergie in den Resonator gestört wurde. Daraufhin wurden systematisch mögliche Ursachen dieser Störung untersucht und das Spektrometer optimiert. Mit diesem optimierten Spektrometer wurden Spektren gemessen, welche sowohl qualitativ als auch quantitativ gut mit den zu erwartenden Spektren übereinstimmen. Als Nachweisgrenze dieses Spektrometers wurde ein Wert für den Absorptionskoeffizienten alpha von 10^-8 cm-1 bestimmt. Mit dem monochromatischen CRD-Spektrometer war es zudem möglich, isotopenspezifische Messungen durchzuführen. Für das breitbandige Spektrometer wurde als Strahlquelle eine ASE-Diode (amplified spontaneous emission) verwendet. Dabei handelt es sich um eine inkohärente Strahlquelle. Mittels Messungen nach dem Prinzip der Cavity-Enhanced-Absorptionsspektroskopie wurde die generelle Funktionalität des resonatorgestützten Spektrometers überprüft. Anschließend wurden die wellenlängenabhängigen Abklingsignale des leeren und des mit einem CO2-Luft-Gemisch gefüllten Resonators gemessen und ebenfalls mit den zu erwartenden Spektren verglichen. Qualitativ stimmen die experimentellen Spektren gut mit den zu erwartenden Spektren überein. Für die quantitative Interpretation der Daten wurde ein spezieller Algorithmus entwickelt, der die spektrale Auflösung des Systems berücksichtigt. Mit dem vorgestellten Spektrometer ist so die qualitative und quantitative Interpretation der Spektren möglich. Die Nachweisgrenze des breitbandigen Cavity-Ring-Down-Spektrometers wurde zu einem Wert von alpha = 8x10^-7 cm-1 bestimmt. Der systematischen und der zufällige Fehler der Messungen lagen bei Werten von ca. 1%. Bei diesem Spektrometer handelt es sich um einen Prototyp. Mittels Optimierung des Systems lassen sich sowohl der Wert der Nachweisgrenze als auch die Fehler der Messungen verbessern.
This thesis presents the design, set-up, characterisation and optimization of various spectrometers to be used for the analysis of gases and gas mixtures. The result of this optimization and its further development is a spectrally broadband cavity ring-down spectrometer (CRD spectrometer), which uses an incoherent light source that emits in the near-infrared. The starting point of the development was a spectrometer which is based on classic absorption spectroscopy inside a multipass cell. This spectrometer uses a supercontinuum laser as light source. The advantage of this spectrometer is its compactness. With this spectrometer, the spectra of various gases and a gas mixture were detected in the spectral range of 1500 nm to 1700 nm. The experimentally derived spectra are in good qualitative accordance to expected spectra based on the HITRAN database. Nevertheless, the qualitative interpretation of the data reveals significant systematic and random errors. As a consequence, a different spectroscopic approach was chosen. The method of choice was cavity ring-down spectroscopy. The advantages of this technique are a) the independence from power fluctuations of the light source, b) an effective absorption path length of up to several kilometres, c) absolute measurement of absorber concentration and d) independence of absorption outside of the cavity. As an important intermediate step on the way to the broadband CRD spectrometer, a monochromatic CRD spectrometer was designed, set up and characterised. To effectively couple light into the cavity, the beam parameters have to be matched to the cavity’s mode. Prerequisite of this mode matching is the knowledge of the beam parameters, which were determined experimentally. Despite this mode matching, the coupling of the light into the cavity turned out to be instable. The cause of that disturbance was systematically investigated, which let to an optimization of the system. The spectra measured with this optimized system were in very good qualitative and quantitative agreement with the expected spectra. The limit of detection of this spectrometer was determined to an absorption coefficient alpha of 10^-8 cm-1. Furthermore, isotope-selective measurements were performed. The light source of the broadband CRD spectrometer is an amplified spontaneous emission diode, which is an incoherent light source. The general functionality of the spectrometer was first tested by means of CEAS measurements (cavity enhanced absorption spectroscopy). Afterwards, the wavelength dependent ring-down signals of the empty cavity and the cavity filled with a CO2 air mixture were detected. The qualitative comparison with the expected data shows very good agreement. For the quantitative interpretation of the experimental data, a special algorithm was developed. Thereby the data measured with the presented spectrometer can be interpreted both qualitatively and quantitatively. The limit of detection of the broadband CRD spectrometer was determined to a value of alpha = 8x10^-7 cm-1. The systematic and the random error are in the range of 1 %. The presented spectrometer is a prototype. Therefore the systematic and random error will be improved by further optimization of the spectrometer.

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Powell, Hayley Victoria. « Development and application of evanescent wave cavity ring-down spectroscopy as a probe of biologically relevant interfaces ». Thesis, University of Warwick, 2009. http://wrap.warwick.ac.uk/3186/.

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The application of a hybrid instrument combining Evanescent Wave Cavity Ring-Down Spectroscopy (EW-CRDS) with electrochemical and fluidic methods is described. The electrochemical/fluidic methods were used to induce a surface process, the effects of which were subsequently monitored in situ and in real time with exquisite spectral sensitivity and excellent temporal resolution by EW-CRDS. The well-defined manner in which the surface processes were initiated allowed the extraction of kinetic rate constants by fitting the EW-CRDS data to mathematical models of the surface process coupled to convection-diffusion. The investigations described include: the study of the thermodynamics and kinetics of the adsorption of tris(bipyridine)ruthenium(II) ([Ru(bpy)3]2+) to polypeptide films using EW-CRDS with chronoamperometry; the real-time electrochemistry of cytochrome c immobilised on silica by EW-CRDS with chronoamperometry; the kinetics of adsorption and DNA-assisted desorption of 5,10,15,20-tetra(N-methylpyridinium-4-yl)porphyrin at the silica-water interface using EW-CRDS with an impinging jet flow cell; and the monitoring the adsorption of cationic phospholipid vesicles at the silica-aqueous interface and the interaction of 5,10,15,20-Tetraphenyl-21H, 23H-porphine-p,p′,p″,p′′′-tetrasulfonic acid tetrasodium hydrate with the resulting bilayer also using EW-CRDS with an impinging jet flow cell. The work described in this thesis provides a platform on which EW-CRDS can be used to study dynamics at biointerfaces, such as the association of ions, peptides, proteins and drugs with phospholipid bilayers, the electron transfer between redox enzymes in a biomimetic environment, and the lateral diffusion of protons, ions and proteins at biomembranes. Such studies are essential to the understanding of many important cellular processes in addition to the development and optimisation of a number of bio-inspired technologies.

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Schnippering, Mathias. « Development and application of evanescent wave cavity ring-down spectroscopy for studies of electrochemical and interfacial processes ». Thesis, University of Warwick, 2009. http://wrap.warwick.ac.uk/3787/.

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This thesis is concerned with the application of evanescent wave cavity ring-down spectroscopy (EW-CRDS) and evanescent wave broadband cavity enhanced absorption spectroscopy (EW-BB-CEAS) for studies of electrochemical and interfacial processes. These include nanoparticle adsorption/dissolution, polymer nanoparticle formation and surface-bound electrochemical redox reactions. Different experimental setups have been designed to investigate these systems. EW-CRDS is a surface sensitive technique, which allows absorption measurements at solid/liquid and solid/air interfaces. Surface reactions can easily be monitored in real time. A pulsed or modulated laser beam is coupled into an optical cavity which consists of at least one optical element, in which the beam is total internal reflected. At the position of total internal reflection (TIR), an evanescent field is established with the amplitude decaying exponentially with distance from the boundary. The evanescent field can be exploited to investigate the absorbance properties of the liquid phase in the first few hundred nanometres of the solution above the silica surface. These types of instruments have high temporal resolution (up to 2 kHz repetition rate), coupled with high sensitivity (minimum detectable interfacial absorbance per pass: ~80 ppm) which enables the investigation of a variety of processes relating to fundamental questions in the field of physical chemistry and materials science. The aforementioned sensitivity and resolution make EW-CRDS an ideal tool for those investigations, especially if combined with other techniques such as electrochemistry or microfluidic and hydrodynamic techniques. In this thesis, different instrumentational setups will be discussed. EW-BB-CEAS is another example for a TIR based absorption spectroscopic technique and can give additional spectral information about the investigated surface processes by employing broadband light such as supercontinuum radiation. In this case, the amplified light intensity within the optical cavity is measured rather than the light decay. By employing complementary techniques, such as electrochemistry and atomic force microscopy and by fitting experimental data using finite-element modelling, surface processes can not only be described accurately but also kinetic information such as rate constants for the aforementioned systems can be calculated.

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Hu, Yuxuan. « Radical concentration and temperature measurements in sooting flames by cavity ring-down spectroscopy and laser-induced fluorescence ». Thesis, University of Strathclyde, 2015. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=25917.

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Sooting laminar flames at atmospheric pressure present a very complex chemical environment with numerous sources of interference for optical measurement techniques. Absolute concentration profiles of ¹CH₂ and HCO have been measured under a range of flame conditions in a sooting laminar premixed C₂H₄-air flat-flame by Cavity-Ring Down Spectroscopy performed at wavelengths in the range 615 to 625 nm. Also, concentration profiles of the OH radical have been detected via the band of A² ∑(v' = 0) ← X² ∏(v'' = 0) system by Laser-Induced Fluorescence and quantitatively calibrated by Cavity-Ring Down Spectroscopy. In situ measurements of these radicals in sooting flames have hitherto been lacking and are essential for validation of chemical kinetic models of aromatic hydrocarbon and soot formation in flames. The experimental results are compared to simulated concentration profiles generated using the Appel-Bockhorn-Frenklach mechanism. Temperature profiles obtained using OH LIF thermometry are used in interpreting the CRDS data and as input for flame simulation. Additionally, weak broadband absorption is observed by CRDS in the region between the reaction zone and the onset of soot formation; this may be attributable to low concentrations of large aromatic species.

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Nakaema, Walter Morinobu. « Espectroscopia de cavidade ressonante tipo Ring-DOWN supercontinuum resolvida no tempo para detecção de multicomponentes gasosos ». Universidade de São Paulo, 2010. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-03112010-164529/.

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Neste trabalho, é apresentada uma variação da técnica de espectroscopia por cavidade ressonante tipo ring-down CRDS (do acrônimo em inglês Cavity Ring-Down Spectroscopy) para a obtenção simultânea do espectro de absorção de multicomponentes numa faixa espectral larga do visível. Esta nova técnica se resume no uso do espectro supercontinuum (resultante da irradiação de meios não lineares através de lasers de femtossegundo, ou simplesmente gerada por fontes compactas) como fonte de luz para iluminar a cavidade. Neste contexto são descritas as características dos módulos para a montagem de um MC-SC-CRDS (Multicomponent Supercontinuum Cavity Ring-Down Spectroscopy): os pares de espelhos altamente refletivos, a cavidade ressonante e o sistema de detecção. Alguns problemas relacionados à excitação de multimodos, à luz difusa, ao uso efetivo do intervalo dinâmico de detecção, à baixa resolução do instrumento em resolver linhas estreitas de absorção são situados. Apresentamos os espectros de absorção de H2O (políades 4nu, 4nu + delta ) e O2 (transições proibidas de spin b-X) simultaneamente medidos por essa técnica na faixa do visível, e uma comparação com as linhas de absorção baseadas do banco de dados HITRAN é feita para demonstrar a funcionalidade deste método.
In this work, we present a variation of the technique CRDS (Cavity Ring-Down Spectroscopy) to obtain simultaneously a multicomponent absorption spectrum in a broad visible range. This new approach uses the Supercontinuum (SC) spectrum (resulting from irradiation of nonlinear media by femtosecond lasers, or simply generated by compact sources) as a light source to illuminate the cavity. In this context it is described the features of the modules assembling a MC-SC-CRDS (Multicomponent Supercontinuum Cavity Ring-Down Spectroscopy): a set of high refletivity mirrors, the resonant cavity and the detection system. Some problems related to the multimode excitation, stray light, effective use of the dynamic range of the detector, the poor resolution of the instrument to resolve narrow absorption lines are issued. We present the absorption spectra of H2O (polyads 4nu, 4nu + delta ) and O2 (spin-forbidden b-X branch) measured simultaneously by this technique in the visible range and a comparison with the absorption lines based on HITRAN database is made to demonstrate the functionality of this method.

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Bostrom, Gregory A. « Development of a Portable Cavity Ring-Down Spectroscopic Technique for Measuring Stable Isotopes in Atmospheric Methane ». PDXScholar, 2010. https://pdxscholar.library.pdx.edu/open_access_etds/51.

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Trace gases can have a significant impact on the Earth's climate, and the analysis of changes in these gases and an understanding of how much of these changes are a result of human activity is important for understanding global climate change. Methane (CH4) is the second only to CO2 in radiative forcing over the last 200 years, and its concentration in the atmosphere has more than doubled since 1750. Sources and sinks of CH4 have characteristic isotopic effects, which shift the relative concentration of the methane isotopologues. Spectroscopic techniques for of analysis the isotopic composition of methane have been evolving since the early 1990's, and promise real-time, in-situ measurements that would provide unprecedented information on the methane atmospheric cycle. Here we present our development and results of a new optical spectroscopic isotope ratio instrument using cavity ringdown spectroscopy in the near IR region using the ν2+2ν3 overtone band. This region has limited interference from other molecules, and an advantageous juxtaposition of a 13CH4 triplet, and a single 12CH4 peak, allowing near-simultaneous measurement of both isotopologues. We present the results of two datasets showing high linearity over a wide range of isotope ratios, which achieved a precision of ±4 /. We present analysis of the data and consider the effects of temperature and molecular interference.

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Sobanski, Nicolas [Verfasser]. « Investigation of day- and night-time NOx/VOCs coupling using thermal dissociation cavity ring-down spectroscopy / Nicolas Sobanski ». Mainz : Universitätsbibliothek Mainz, 2016. http://d-nb.info/112182627X/34.

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CAVALCANTI, FABIO. « Desenvolvimento de um laser pulsado com emissão em 1053 nm para utilização na técnica de "Cavity Ring-Down Spectroscopy ». reponame:Repositório Institucional do IPEN, 2014. http://repositorio.ipen.br:8080/xmlui/handle/123456789/11790.

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Submitted by Claudinei Pracidelli (cpracide@ipen.br) on 2014-11-10T10:46:11Z No. of bitstreams: 0
Made available in DSpace on 2014-11-10T10:46:11Z (GMT). No. of bitstreams: 0
Dissertação (Mestrado em Tecnologia Nuclear)
IPEN/D
Instituto de Pesquisas Energeticas e Nucleares - IPEN-CNEN/SP

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Cavalcanti, Fabio. « Desenvolvimento de um laser pulsado com emissão em 1053 nm para utilização na técnica de \"Cavity Ring-Down Spectroscopy\" ». Universidade de São Paulo, 2014. http://www.teses.usp.br/teses/disponiveis/85/85134/tde-14102014-145230/.

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Neste trabalho, foi desenvolvido um laser pulsado utilizando um chaveador-Q passivo em uma cavidade com a tecnologia de controle de modo por duplo-passo. Utilizando um cristal de Nd:LiYF4 com 0,8 mol% de dopagem, foi possível gerar um pulso com duração de 5,5 ns (FWHM), com 1,2 mJ de energia e potência pico de 220 kW para utilização na técnica Cavity Ring-Down Spectroscopy (CRDS). A técnica (CRDS), que pode ser traduzida por espectroscopia de cavidade ressonante, é utilizada para medida de espectros de absorção de gases, líquidos e sólidos. Com a técnica CRDS é possível medir perdas com altíssimo grau de precisão, ressaltando sua sensibilidade que é confirmada pela utilização de espelhos com alta refletividade. Foram avaliadas, com essa técnica, as perdas por reflexão e espalhamento de materiais transparentes. Após a calibração da cavidade ressonante, foi possível medir as perdas nas amostras com resolução de até 0,045%, sendo o valor máximo alcançado de 1,73%. Essa calibração foi possível, pois obteve se um tempo de decaimento de aproximadamente 20 μs com a cavidade desobstruída. Também foi conseguido um método de determinação do índice de refração dos materiais transparentes com precisão de cinco casas decimais.
In this work, a pulsed and Q-switched laser resonator was developed using the double-beam mode-controlling technique. A Nd:LiYF4 crystal with 0,8mol% of doping concentration was used to generate a giant pulse with duration of 5,5 ns (FWHM), 1,2 mJ of energy and 220 kW peak power for the Cavity Ring-Down Spectroscopy (CRDS) technique. The CRDS technique is used to measure absorption spectra for gases, liquids and solids. With the CRDS technique it is possible to measure losses with high degree of accuracy, underscoring the sensitivity that is confirmed by the use of mirrors with high reflectivity. With this technique, the losses by reflection and scattering of transparent materials were evaluated. By calibrating the resonant cavity, it was possible to measure the losses in the samples with resolution of 0,045%, the maximum being reached by 1,73%. The calibration was possible because there was obtained to measure a decay time of approximately 20 μs with the empty cavity. Besides was obtained a method for determining the refractive index of transparent materials with accuracy of five decimals.

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Mercier, Xavier. « Mesure de concentrations absolues d'espèces réactives minoritaires dans les flammes par la technique d'absorption Cavity Ring Down Spectroscopy (CRDS) ». Lille 1, 2000. http://www.theses.fr/2000LIL10154.

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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

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Kiwanuka, Ssegawa-Ssekintu. « Supercontinuum radiation for ultra-high sensitivity liquid-phase sensing ». Thesis, University of Cambridge, 2014. https://www.repository.cam.ac.uk/handle/1810/245137.

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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.

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Phung, Viet Tiep. « Cavity ring-down spectroscopy of astrophysically relevant molecular species, toward quantitative and high resolution studies using spectro-temporal properties of high finesse cavities ». Thesis, Université Paris-Saclay (ComUE), 2016. http://www.theses.fr/2016SACLS188/document.

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Le principal objectif de ce travail de thèse a été de développer de nouvelles techniques de spectroscopie moléculaire afin obtenir de nouvelles données spectroscopiques dans le visible et le proche infrarouge pour des molécules, radicaux ou ions d’intérêt astrophysiques. La première partie de ce travail a consisté en l’étude d’harmoniques élevés, très faibles en intensité, de bandes vibrationnelles de la molécule HC₃N (cyanoacetylène), par la technique de spectroscopie CRDS. La deuxième partie a consisté en l’étude spectroscopique d’espèces instables radicalaires. Pour cela, une décharge inductive Radio Fréquence a été couplée au montage CRDS. Le plasma ainsi créé a été caractérisé et sa capacité à produire des anions a été démontrée via notamment la mesure quantitative du rapport C₂ / C₂⁻pour une grande variété de conditions expérimentales. De même, une analyse spectroscopique quantitative a été menée sur les radicaux isotopomères ¹⁴NH₂ et ¹⁵NH₂. Cette étude valide certaines hypothèses faites dans de précédents travaux ayant permis de mesurer le rapport isotopique ¹⁵N/¹⁴N dans les comètes, pour la première fois à partir de raies d’émission de ces 2 isotopomères portant un groupe amino. La troisième et dernière partie de ce travail a consisté en le développement d’une nouvelle technique expérimentale appelée Broad-Band Dual Etalon Frequency COMb. Cette technique expérimentale basée sur l’utilisation de 2 cavités optiques de haute finesse devrait permettre d’obtenir une spectroscopie avec une résolution spectrale ultime non limitée par la source laser nanoseconde large bande mais par l’intervalle spectral libre des cavités de haute finesse utilisées
The main objective of this PhD was to develop spectroscopic techniques using high finesse optical cavities. These were applied to the measurement of quantitative spectroscopic data for neutral, radical and ionic molecular species of astrophysical interest in the near infrared and visible spectral range. The first part was devoted to the measurement of the oscillator strength of high vibrational overtone bands of the cyanoacetylene (HC₃N) molecule with the Cavity Ring Down Spectroscopy (CRDS) technique. The second part was devoted to the study of the spectroscopy of transient neutral and ionic species. For that, an inductively radio frequency (RF) discharged has been coupled to the CRDS set up. The pertinence of this plasma to efficiently produce anions was demonstrated via the quantitative measurement of the C₂ / C₂⁻ ratio in a wide variety of conditions. A quantitative spectral analysis of the radical isotopomers ¹⁴NH₂ and ¹⁵NH₂ was also performed for the first time. This study provides experimental data that will allow to better constraint the ¹⁵N/¹⁴N isotopic ratio in comets through the emission lines of these two amino bearing isotopomers. The third and last part of the work was devoted to the development of a CRDS scheme called Broad Band Dual Etalon Frequency Comb Ring Down Spectroscopy. This new heterodyne technique, based on the use of the microsecond frequency combs generated by two high finesse optical cavities, should allow performing molecular spectroscopy with ultrahigh spectral resolution. First proof experiments were performed and perspective’s for improvement of the method is provided

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Lu, Jessica Weidgin. « Dynamics of Atmospherically Important Triatomics in Collisions with Model Organic Surfaces ». Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/77045.

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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.

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Perevalov, Boris. « Le spectre d'absorption du dioxyde de carbone dans le proche infrarouge (1. 4-1. 7 micro) : Cavity Ring Down Spectroscopy, modélisation globale et bases de données ». Grenoble 1, 2009. http://www.theses.fr/2009GRE10028.

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"Les spectres d'échantillons naturel et enrichi en BC du dioxyde de carbone ont été enregistrés entre 5851 et 7045 cm-l par CW-Cavity Ring Down Spectroscopy à très haute senisbilité. Environ 8000 transitions appartenant à huit isotopologues de CO2 e2C1602, 13CI602, l60l2C180, l60l2C170, l6013CI80, l6013C170, l3C1802, 17013CI80) ont été mesurées avec une précision estimée de 1 x 10-3 cm-l. Les paramètres spectroscopiques ont été obtenus pour un total de 238 bandes, la plupart nouvellement observées. Un certain nombre de résonances ont été observées et identifiées. Les données expérimentales disponibles dans la littérature et celles obtenues au cours de cette thèse ont été utilisées pour améliorer les paramètres du modèle effectif qui reproduit les positions avec un accord proche de leurs incertitudes expérimentales. Les intensités de 2039 et 952 raies ont été mesurées pour 13C1602 et l2C1602' Dans le cas de l2Cl602 la plupart des intensités mesurées appartiennent aux bandes perpendiculaires et "interdites". Ces données expérimentales, combinées à des données publiées, ont été utilisées pour améliorer les param~tres du moment dipolaire effectif de ces deux isotopologues. L'ensemble de ces paramètres reproduit les intensités mesurées aux incertitudes expérimentales près. Quatre cas de résonance interpolyade ont été observés pour la première fois dans le cas de CO2. Cette thèse apporte une contribution importante aux bases de données spectroscopiques du dioxyde de carbone: CDSD et HITRAN. Les résultats obtenus ont été intégrés dans la base de données HITRAN qui fait référence pour la physique de l'atmosphère. "
The CW-CRDS spectra of naturaI and 13C-enriched carbon dioxide in the 5851-7045 cm-I region were analyzed inc1uding the previously investigated 6130-6750 cm-l region which was re-examined in order to reduce the fraction ofunassigned lines. About 8000 line positions belonging to 8 CO2 isotopologues e2C1602, 13CI602' l6012CI80, l6012C170, l6013CI80, l6013C170, 13CI802, l7013CI80) were newly measured with estimated accuracy of 1 X 10-3 cm-l. Only about 5% of lines remained unassigned. The rovibrational parameters were retrieved for a total of 238 bands belonging to eight CO2 isotopologues. A number of resonance intersections were observed and identified. The newly observed line positions were added to the input datasets in order to refme the effective Hamiltonian parameters for six CO2 isotopologues. The fitted sets of effective Hamiltonian parameters reproduce the line positions close to their experimental uncertainties. The line strengths of 2039 and 952 transitions were measured for 13C1602 and l2Cl602 isotopologues in the 1. 6 J. 1m region. Ln the case of l2Cl602 isotopologue the most part of the measured intensities belong to weak perpendicular and "forbidden" bands. The present results were gathered with the selected intensity data reported in the literature in order to refme the effective dipole moment parameters. The fitted sets of effective dipole moment parameters reproduce the experimentalline within their uncertainties. Four occurrences of interpolyad resonance interaction were evidenced for the first time in the case of carbon dioxide. The present work makes an important contribution in the development of the CDSD and HITRAN databases for CO2

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Kwon, Deokhyeon. « Optical and physicochemical properties of secondary organic aerosol and aerosol generated from humic substances ». Diss., University of Iowa, 2018. https://ir.uiowa.edu/etd/6455.

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A great deal of attention has been paid to brown carbon aerosol in the troposphere because it can both scatter and absorb solar radiation, thus affecting the Earth’s climate. However, knowledge of the optical and chemical properties of brown carbon aerosol is still limited. In this thesis, we have investigated different aspects of the optical and physicochemical properties of various brown carbon aerosol samples of potential atmospheric importance. First, reactions involving the di-carbonyl species methylglyoxal (MG) have been previously suggested as an important pathway for the production of secondary organic aerosol (SOA) in the atmosphere. Reaction in an aqueous inorganic salt solution, such as ammonium sulfate (AS), leads to the formation of light-absorbing brown carbon (BrC) product. In this thesis work, we employed a variety of experimental approaches to investigate the optical and physicochemical properties of BrC aerosol generated from this AS-MG reaction (BrC (AS/MG)). Optical properties of the dried BrC (AS/MG) aerosol particles were studied by Fourier transform infrared (FTIR) extinction spectroscopy in the mid-infrared region, cavity ring-down spectroscopy (CRDS) at 403 nm in the visible, and by measuring the light scattering phase function and polarization profiles at two different visible wavelengths, 532 and 402 nm. In addition, we used UV−vis spectroscopy to measure the mass absorption coefficient (MAC) of the solution-phase reaction products. The different optical properties were measured as a function of reaction time for a period of up to 22 days. The UV-vis absorption spectra showed a clear increase in measured MAC in the visible and near UV as the solution aged. However, analysis of the light scattering data showed no significant differences between AS and BrC aerosol in the derived refractive indices at either 532 or 402 nm, even for the longest reaction times. The FTIR extinction spectra was modeled in a Mie theory simulation to derive the complex refractive index in the mid-IR range (7000-800 cm−1); the results showed no significant changes in either the real or the imaginary parts of the refractive indices for BrC (AS/MG) aerosol particles when compared to unreacted AS aerosol. From the CRDS extinction data, the optical constants for BrC (AS/MG) particles at 403 nm were also determined through a Mie theory based analysis. The retrieved real index of refraction at 403 nm is n = 1.551 ± 0.005, with an imaginary index value of k = 0.000 ± 0.002; these values do not appear to change significantly with aging time over the course of 22 days and are not markedly different from the AS aerosol values. The small imaginary index value suggests that BrC (AS/MG) aerosol formed from this pathway may not significantly contribute to warming. In addition, CRDS measurements of the BrC (AS/MG) aerosol extinction at 403 nm as a function of particle size show a significant deviation from Mie theory simulations for particles with diameters of ≳500 nm, probably as a result of non-spherical particle shape effects. We also employed atomic force microscopy (AFM)-based IR spectroscopy to investigate the morphology and chemical composition of single SOA particles. AFM analysis of the particle morphology shows that a significant fraction of BrC (AS/MG) particles with diameters of ≳500 nm are non-spherical in shape, consistent with our observed breakdown in the applicability of Mie theory for larger particles. In addition to these measurements, we have characterized additional physicochemical properties of the BrC (AS/MG) aerosol particles including hygroscopic growth using a tandem-differential mobility analyzer. Compared to AS, BrC aerosol particles are found to have lower deliquescence relative humidity (DRH), efflorescence relative humidity (ERH), and hygroscopic growth at the same relative humidity values. Second, we investigated the optical properties of the water soluble products of limonene BrC generated from ozonolysis of d-limonene with further aging by AS. Optical constants for the dried limonene BrC aerosol product were measured at 403 nm by CRDS over the course of 9 days of aging. While the fresh limonene BrC aerosol showed a significant non-zero absorption index, the aged samples showed absorption index values consistent with zero. This result was somewhat unexpected because UV-vis absorption spectra of the bulk reaction solution showed a continued increase in absorption as the solution aged. One possible explanation for this result is that there could be an increase in the fraction of volatile chromophores as the solution ages, that are then removed in the aerosol drying process. Third, we investigated optical properties and chemical compositions of several humic substance (HS) reference samples including humic acid (HA) and fulvic acid (FA) standards by CRDS, UV-vis spectroscopy, elemental analysis, and 13C NMR spectroscopy. Measurements of the optical properties of HS is important in atmospheric science, because it is thought that HS samples have similar optical properties to organic materials, such as HUmic-Like Substances (HULIS), that exist in clouds, fogs, rainwater, and atmospheric aerosol. The humic acid aerosol samples generally showed higher absorption index values than the fulvic acid aerosol samples. We also found a correlation between the absorption index and chemical composition, with the value for k generally increasing with both increasing carbon-to-oxygen atomic ratio and sample aromaticity. In addition, we compared our measured optical constants for the HS aerosol samples with results from previous studies of field collected HULIS. The absorption index values for the fulvic acid aerosol samples give a better match than the humic acid samples when compared to the results from the field collected samples. Overall, these studies provide new details of the optical and physicochemical properties of a class of brown carbon organic aerosol which may have important implications for atmospheric chemistry and climate.

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Chase, Tanya. « Greenhouse gas detection using cavity enhanced absorption spectroscopy and cavity ring-down spectroscopy : trace detection of CH₄, CO₂ and N₂0 in ambient air, standard gas samples and in the headspace of soils ». Thesis, University of Bristol, 2015. http://ethos.bl.uk/OrderDetails.do?uin=uk.bl.ethos.686246.

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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.

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Ouimet-Storrs, Alexandre. « Development of a cavity ring-down spectroscopy setup and validation with carbon-hydrogen radical measurements in an argon and acetylene direct currentb low-pressure glow discharge plasma ». Thesis, McGill University, 2006. http://digitool.Library.McGill.CA:80/R/?func=dbin-jump-full&object_id=99004.

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Cavity ring-down spectroscopy (CRDS) is a novel, accurate, sensitive and non-intrusive laser-based technique using multiple-paths molecular absorption to measure weak absolute concentrations of atoms or molecules (ppm range or better). In CRDS, a laser pulse is coupled into an optical cavity equipped of highly reflective mirrors mounted at both ends and containing the absorbing medium. The laser pulse experiences numerous round trips inside the cavity thus considerably increasing the absorption path. The decay of the laser pulse intensity leaking out of one of the cavity mirrors is monitored in real-time and the concentration of the species is obtained by fitting a Beer-Lambert's decay to the measured signal. The resulting signal is an exponentially decaying function with a 1/e cavity ring-down (tau), proportional to the absolute concentration of the absorbing species.
The main objective of this Master's project was to develop a CRDS system to be used for the study of plasma-surface interactions. The CRDS cavity measures 92 cm in length and has a spatial resolution of 1 mm2, and is flexible enough in its design to accommodate a low-pressure glow discharge or a miniature atmospheric pressure plasma torch at the centre of the cavity. In this study, the low-pressure glow discharge plasma is used to produce CH radicals from a 95% Ar - 5% C2H2 gas mixture. Preliminary optical emission spectroscopy- (OES) measurements near 431 rim indicated the presence of CH radicals in the plasma. For the CRDS experiments, the electronic transition A2Delta ← X2pi of the CH radical was probed using a tunable dye laser (10Hz, 5 ns pulse, 0.8 cm -1 linewidth) tuned to 431.131 nm, and at a pulse energy of approximately 30-40 muJ. The CRDS system was able to measure CH radical concentrations ranging from 1.78x1012cm-3 to 2.18 x10 12 cm-3.

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Lelaidier, Tony. « Organic semiconductor characterisation by scanning tunnelling microscopy and optical spectroscopy ». Thesis, Aix-Marseille, 2016. http://www.theses.fr/2016AIXM4032/document.

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Les propriétés électroniques et d'autoassemblage de deux composés organiques, le DHTAP et le bis-pyrène, ont été étudiées par microscopie à effet tunnel (STM), sous ultra-vide et à basse température. Les propriétés optiques ont été étudiées par spectroscopie en cavité résonnante (CRD), également sous ultravide.La croissance du DHTAP a été étudiée sur différents métaux nobles. La croissance du bis-pyrène a été étudiée sur Au(111). Dans chaque cas, les conditions de température idéales pour la formation d’une première couche organisée ont été déterminées. Différents modèles sont proposés pour les structures observées en première couche. La formation de la seconde couche moléculaire à également été étudiée.L'évolution des propriétés optiques, étudié par CRD, du bis-pyrène déposé sur du verre borosilicate combinée aux informations obtenues par STM ont permit d’associer ces modifications aux interactions des moments dipolaires de transition des molécules de la première et de la seconde couche et on également permit de déterminer le mode de croissance.Finalement, la possibilité d’induire des modifications chimique de la molécule de DHTAP, intégrée dans une couche auto-assemblée, en utilisant le courant tunnel du STM a été observé. Il s’avère que la molécule de DHTAP intégrée en première couche peut subir une double déshydrogénation pour conduire à la formation d’un composé identifié comme étant le 5,7,12,14-tetraazapentacene (TAP). En seconde couche, la formation de deux radicaux, en plus du TAP, a été observé. La molécule de TAP présente un certain intérêt du fait qu’elle n’est pas synthétisable pas les méthodes conventionnelle de chimie organique
Electronic and self-assembling properties of two organic compound, the DHTAP and the bis-pyrene, have been studied by the means of low temperature scanning tunnelling microscopy (STM) under ultrahigh vacuum conditions. Optical properties have been studied by cavity ring-down (CRD) spectroscopy, also under ultrahigh vacuum conditions.The growth of DHTAP has been studied on different metallic substrate. The growth of bis-pyrene has been studied on Au(111). In each case, the optimal temperature conditions for the formation of a well-ordered first monolayer have been determined. The formation of second monolayers has also been studied. The evolution of the optical properties, studied by CRD, of bis-pyrene deposited on borosilicate glass combined with information obtained from STM allow us to identify these modifications as interactions between transition dipole moments of molecules in the first and in the second layer, and also determine the growth mode.Finally, the possibility to induce chemical modification of DHTAP molecules embedded in an ordered monolayer using the tunnelling current of the STM has been studied. It appears that the molecule embedded in the first ML can be doubly dehydrogenated which leads to the formation of a compound identified as 5,7,12,14-tetraazapentacene (TAP). In the second layer, the formation of two radicals in addition to the TAP has been observed. The TAP molecule is interesting because of that it cannot be synthesized using common organic chemical methods

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Johnson, Jennifer E., et Chris W. Rella. « Effects of variation in background mixing ratios of N2, O2, and Ar on the measurement of δ 18O–H2O and δ 2H–H2O values by cavity ring-down spectroscopy ». COPERNICUS GESELLSCHAFT MBH, 2017. http://hdl.handle.net/10150/625771.

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Cavity ring-down spectrometers have generally been designed to operate under conditions in which the background gas has a constant composition. However, there are a number of observational and experimental situations of interest in which the background gas has a variable composition. In this study, we examine the effect of background gas composition on a cavity ring-down spectrometer that measures δ18O–H2O and δ2H–H2O values based on the amplitude of water isotopologue absorption features around 7184 cm−1 (L2120-i, Picarro, Inc.). For background mixtures balanced with N2, the apparent δ18O values deviate from true values by −0.50 ± 0.001 ‰ O2 %−1 and −0.57 ± 0.001 ‰ Ar %−1, and apparent δ2H values deviate from true values by 0.26 ± 0.004 ‰ O2 %−1 and 0.42 ± 0.004 ‰ Ar  %−1. The artifacts are the result of broadening, narrowing, and shifting of both the target absorption lines and strong neighboring lines. While the background-induced isotopic artifacts can largely be corrected with simple empirical or semi-mechanistic models, neither type of model is capable of completely correcting the isotopic artifacts to within the inherent instrument precision. The development of strategies for dynamically detecting and accommodating background variation in N2, O2, and/or Ar would facilitate the application of cavity ring-down spectrometers to a new class of observations and experiments.

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Magnani, Cecilia. « Monitoraggio di CO2 e CH4 presso il "Centro aeronautica militare di montagna" sulla vetta del Monte Cimone ». Bachelor's thesis, Alma Mater Studiorum - Università di Bologna, 2019. http://amslaurea.unibo.it/17680/.

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Questo elaborato di tesi si concentra sull’analisi del complesso lavoro di monitoraggio e studio dei gas ad effetto serra, in particolare anidride carbonica (CO2) e metano (CH4), effettuato dal CAMM (Centro Aeronautica Militare di Montagna), stazione operativa del Servizio Meteorologico dell’Aeronautica Militare di Sestola (Mo). Tramite un particolare Greenhouse Gas Analyzer, il PICARRO G2301, che sfrutta la tecnologia CRDS (Cavity Ring Down Spectroscopy), viene garantito il monitoraggio delle sole caratteristiche spettrali di interesse. La CRDS è una tecnica basata su un principio di misurazione della velocità di decadimento esponenziale dell’intensità luminosa di un laser all’interno di una cavità anulare. Gli studi effettuati a questo proposito risultano fondamentali in un contesto climatico, ma anche sociale e politico, attualmente critico. L’aumento delle concentrazioni di gas serra, influenzato dalle sorgenti di natura antropica, è un fattore determinante dell’aumento dell’effetto serra e quindi del conseguente incremento della temperatura media globale, che potrebbe condurre ad ingenti conseguenze climatiche. Il CAMM è la seconda stazione al mondo ritenuta di rilevanza globale dall’Organizzazione Meteorologica Mondiale, all’interno del programma GAW (Global Atmosphere Watch); dal 1979 la stazione effettua misure a campionamento continuo delle concentrazioni di anidride carbonica, possiede quindi 40 anni di misure che compongo la più lunga serie storica d’Europa, da cui si può dedurre in maniera evidente il costante progressivo aumento della concentrazione di tale gas nell’atmosfera. Dagli ultimi risultati, in particolare, il tasso di crescita annuale per il Monte Cimone risulta superiore a 1.81 ppm/anno, andamento sovrapponibile ai relativi dati registrati dalle altre stazioni del GAW, conferma dell’estrema valenza e rappresentatività globale della stazione.

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Neil, Simon R. T. « Condensed-phase applications of cavity-based spectroscopic techniques ». Thesis, University of Oxford, 2012. http://ora.ox.ac.uk/objects/uuid:4431e46e-1226-4950-aa5d-ce22e0309ba9.

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This thesis describes the development and application of condensed-phase cavity-based spectroscopic techniques - namely cavity ring-down spectroscopy (CRDS); cavity enhanced absorption spectroscopy (CEAS); broadband cavity enhanced absorption spectroscopy (BBCEAS) and evanescent wave (EW) variants of all three. The recently-developed cavity technique of EW-broadband cavity enhanced absorption spectroscopy (EW-BBCEAS) has been used—in combination with a supercontinuum source (SC) and a sensitive, fast readout CCD detector—to record of the full visible spectrum (400–700 nm) of a silica-liquid interfacial layer (with an effective thickness ca. 1 µm), at rapid acquisition rates (> 600 Hz) that are sufficient to follow fast kinetics in the condensed phase, in real time. The sensitivity achieved (A_min= 3.9 x 10^-5) is comparable with previous EW-CRDS and EW-CEAS studies, but the spectral region accessed in this broadband variant is much larger. The study of liquid|air interfaces using EW cavity-based techniques is also illustrated for the first time. The first application of BBCEAS to the analysis of microfluidic samples, flowing through a microfluidic chip, is illustrated. Proof-of-principle experiments are presented, demonstrating the technique’s ability to provide full visible broadband spectral measurements of flowing microfluidic droplets, with both high detection sensitivity (α_min < 10^-2 cm^-1) and excellent spatial and temporal resolution: an SC light source and sensitive, fast readout CCD allowed measurement repetition rates of 273 Hz, whilst probing a very small sample volume (ca. 90 nL). A significant portion of this thesis is devoted to demonstrating the powerful capabilities of CEAS, CRDS and BBCEAS in monitoring radical recombination reactions and associated magnetic field effects (MFEs) in solution. The efficacy of CEAS as a high-sensitivity MFE detection method has been established in a proof-of-principle study, using narrow band CEAS in combination with phase-sensitive detection: MFE-induced absorbance changes of ca. 10^-6 could be detected using the modulated CEAS technique and the data are shown to be superior to those obtained using conventional transient absorption (TA) methods typically employed for MFE measurements. The powerful capabilities of CRDS in monitoring radical recombination reactions and associated MFEs are also demonstrated. In particular, a pump-probe CRDS variant allows not only high sensitivity (A_min on the order 10^-6), but also sub-microsecond time-resolution. Combined, these features represent significant advantages over TA. Finally, SC-BBCEAS is used to measure full visible spectra of photoinduced reactions and their MFEs. The applicability of this approach to in vitro MFE studies of Drosophila cryptochrome is demonstrated—the results mark the first in vitro observation of a magnetic field response in an animal cryptochrome, a key result supporting the hypothesis that cryptochromes are involved in the magnetic sense in animals.

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Fischer, Tobias. « Development of dual mode labels for the quantitative analysis of surface functional groups with XPS and fluorescence ». Doctoral thesis, Humboldt-Universität zu Berlin, 2017. http://dx.doi.org/10.18452/17764.

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In dieser Arbeit sollte eine Derivatisierungsmethode entwickelt werden, die die duale Quantifizierung funktioneller Gruppen an Oberflächen mittels Röntgenphotoelektronenspektroskopie (XPS) und Fluoreszenz ermöglicht. Verschiedene Farbstoffe, die robuste Fluoreszenzeigenschaften mit hohen Fluorgehalten für XPS kombinieren, wurden auf ihre selektive Reaktion mit Aminogruppen getestet und der Prototyp einer tiefergehenden Analyse auf einer Oberfläche unterzogen. Durch Fluoreszenzlöschung konnten die Möglichkeiten der bimodalen Analyse nur begrenzt abgeschätzt werden, obwohl in XPS und Fluoreszenz intensive Signale gemessen wurden. Die Herstellung der Modelloberflächen mittels Gasphasenabscheidung von Silanen konnte durch Kontaktwinkelmessungen schrittweise optimiert werden. Die Kombination zweier Monoalkoxysilane ermöglichte die Herstellung von Oberflächen mit variabler Funktionalgruppendichte. Nach Reaktion mit dem dualen Marker ließen sich die Messungen aus XPS und Fluoreszenz mindestens über eine Größenordnung korrelieren. Durch Synchrotron-XPS (SR-XPS) und Röntgenfluoreszenz unter Totalreflektion (TXRF) konnte eine absolute und rückführbare Quantifizierung erzielt werden. Weitere Modelloberflächen auf Basis von Trialkoxysilanen zeigten, dass bei anwendungsnahen Proben Fluoreszenzlöschung auftritt. Diese konnte in einem gewissen Maße mittels Fluoreszenzlebensdauer berechnet werden. Darüberhinaus konnte mit der Photometrie eine unabhängige Methode gefunden werden, die die Quantifizierung des Farbstoffs an der Oberfläche in hoher Präzision ermöglicht und mit Hilfe der XPS auch der funtionellen Gruppen. Die Cavity Ring-Down Spektroskopie (CRDS) wurde als Laserbasierte Methode zur empfindlichen und ortsaufgelösten Messung der Absorption auf transparenten Substraten untersucht und erste vielversprechende Ergebnisse gewonnen. Weiterhin wurde ein modulares Farbstoffsystem entwickelt, das sowohl Variation der spektralen als auch der Bindungseigenschaften erlaubt.
This work aimed on the development of dual-mode labelling method that combines X-ray photoelectron spectroscopy (XPS) with fluorescence measurements for surface functional group quantification. Label dyes combining robust fluorescence properties with high fluorine contents were investigated towards their selective reaction with surface amino groups and the lead candidate subjected to detailed analysis on a surface. Fluorescence quenching precluded a detailed investigation of the capabilities of dual-mode labelling, despite providing sufficient signal in XPS and fluorescence scanning. The fabrication of surfaces using vapour deposition (VD) of silanes in toluene was optimized under aid of contact angle measurements. Binary mixtures of mono-alkoxy silanes were used to prepare surfaces with variable functional group density. Treatment with the label dye showed that XPS and fluorescence provide a linear overlap in signal generation over at least one order of magnitude. The combination of synchrotron radiation XPS (SR-XPS) and total reflection X-ray fluorescence spectroscopy (TXRF) provided an absolute and traceable quantification . Different model surfaces based on trialkoxy silanes showed strong fluorescence quenching. A fluorescence lifetime based correction was developed to account for such quenching effects. Additionally, the application of spectrophotometry provided a independent method of quantification for the surface bound dye and in combination with information obtained from XPS, to determine the surface functional group density. With cavity ring-down spectroscopy (CRDS), a laser based technique for highly sensitive and spatially resolved absorption measurements on transparent substrates could be developed and applied in a proof-of-concept. A modular system for the fabrication of label dyes with adjustable spectral properties and different binding sites was investigated using prototype candidates to prove the general applicability of such systems.

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Davies, Nicholas William. « The climate impacts of atmospheric aerosols using in-situ measurements, satellite retrievals and global climate model simulations ». Thesis, University of Exeter, 2018. http://hdl.handle.net/10871/34544.

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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.

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Li, Jing. « Applications of optical-cavity-based spectroscopic techniques in the condensed phase ». Thesis, University of Oxford, 2014. http://ora.ox.ac.uk/objects/uuid:d6a0c476-e67f-4390-a63a-e3cb9e60bf2c.

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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.

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Sebastian, Ananthu. « Noise dynamics in multi-Stokes Brillouin laser ». Thesis, Rennes 1, 2020. http://www.theses.fr/2020REN1S068.

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La diffusion Brillouin stimulée (SBS) est un processus d'interaction cohérent, pour lequel la lumière est diffusée à partir des ondes acoustiques générées optiquement. Les lasers Brillouin suscitent un très grand intérêt pour leur capacité à produire des largeurs de raie ultra cohérentes. Cette thèse est consacrée à la compréhension des propriétés de bruit des lasers à fibre Brillouin en anneau, fonctionnant avec de multiples ordres de Stokes. Tout d'abord, nous présentons une technique basée sur la méthode de ringdown de la cavité, qui permet de caractériser le coefficient de gain Brillouin directement à partir du sondage de la cavité laser. Ses avantages sont d'obtenir des paramètres à partir d'une seule expérience avec de faibles puissances optiques (quelques 10 milliwatts) pour des cavités courtes (quelques mètres de long, ou cavités intégrées). Deuxièmement, il est démontré qu'une largeur de raie intrinsèque de quelques dizaines de mHz peut être facilement obtenue en cascadant deux lasers Brillouin non résonants (pour lesquels la pompe effectue un seul passage à l'intérieur de la cavité). Afin d'obtenir ces résultats, la stabilité à long terme a été améliorée en utilisant une boucle d'asservissement de type Pound Drever Hall, ce qui nous permet de comparer nos résultats analytiques et expérimentaux. Malheureusement, nous n'avons pas exploré les limites fondamentales de la réduction du bruit en raison du plancher de bruit de notre banc de mesure. Troisièmement, un des travaux majeurs de cette thèse est l'étude analytique et expérimentale des propriétés du bruit, y compris le bruit de fréquence et le bruit relatif d'intensité, d'un laser Brillouin résonant (pour lequel, les ondes de pompe et de Stokes sont résonantes à l'intérieur de la cavité). En particulier, les impacts du facteur de qualité de la cavité fibrée en anneau, le désaccord de gain Brillouin ont été évalués très précisément sur les caractéristiques du RIN du laser telles que la réduction de l'amplitude du bruit et la fréquence de relaxation. Nous soulignons le fait que de nombreuses caractéristiques du bruit de fréquence sont liées aux propriétés du RIN par un couplage entre l'intensité et la phase. Nous montrons que le processus en cascade modifie la dynamique du laser Brillouin par rapport à celle d'un laser Brillouin monomode avec une seule composante de Stokes de premier ordre. Nos résultats expérimentaux sont en excellent accord avec nos simulations, obtenues grâce à notre système non linéaire décrivant le fonctionnement d'un laser Brillouin multi-Stokes. Cette bonne concordance est principalement due à notre capacité : à obtenir des valeurs très précises des paramètres de la cavité et du coefficient de gain Brillouin en utilisant la technique CRDM ; à atteindre une stabilité à long terme (plusieurs dizaines d'heures) ; à contrôler finement le désaccord entre la résonance de Stokes du laser et la fréquence du maximum de gain Brillouin. Nous démontrons expérimentalement pour la première fois que le bruit de fréquence est dégradé en présence d'une diffusion Brillouin anti-Stokes. Nous montrons également qu'un désaccord de gain de l'ordre de quelques centaines de kHz peut dégrader la réduction du bruit d'intensité ou également augmenter la largeur de raie par un couplage amplitude-phase. Toutes ces observations très fines nous permettent donc de fixer les limites fondamentales de tels systèmes laser comme : l'augmentation du bruit due aux ordres anti-Stokes ; le rôle du bruit de pompe et son interrelation possible avec la finesse de la cavité ; l'effet du désaccord inhérent aux ordres de Stokes plus élevés. Toutes ces conclusions sont les clés de la conception et de l'ingénierie de ces lasers à fibre Brillouin, qui suscitent actuellement beaucoup d'intérêt comme en témoignent les travaux en cours dans la communauté scientifique. Cette thèse de doctorat contribue à une meilleure compréhension des lasers Brillouin multi-Stokes
Stimulated Brillouin Scattering (SBS) is a coherent interaction process in which light is scattered from optically generated acoustic waves. It is a powerful tool for microwave and optical signal processing, distributed sensing and spectroscopy. Brillouin lasers are attracting a lot of interest for their ability to produce ultra coherent linewidths. This thesis is devoted to the understanding of noise properties of Brillouin fiber ring lasers, operating with multiple Stokes orders. First, we present a technique based on the cavity ring-down method, which allows to characterize the Brillouin gain coefficient directly from probing the laser cavity. Its advantages are to obtain parameters from a single experiment with low optical powers (some 10 milliwatts) for short cavities (a few meters long, or integrated cavities). Secondly, it is shown that an intrinsic linewidth of a few tens of mHz can be easily obtained by cascading two non-resonant Brillouin lasers (for which the pump performs a single pass inside the cavity). In order to obtain these results, the long-term stability has been improved by using a Pound-Drever-Hall servo loop, which allows us to compare our analytical and experimental results. Unfortunately, we were unable to explore the fundamental limits of noise reduction due to the noise floor of our bench. Thirdly, one of the major works of this thesis is the theoretical and experimental study of the noise properties, including frequency noise and relative intensity noise, of a resonant Brillouin laser (for which pump and Stokes waves are resonant inside the cavity). In particular, the impacts of the fiber-ring-cavity quality factor, Brillouin gain detuning, are evaluated very precisely on the laser RIN features such as amplitude noise reduction and relaxation frequency. We emphasize the fact that many characteristics of the frequency noise are related to the RIN properties by a coupling between intensity and phase. We show that the cascade process modifies the dynamics of the Brillouin laser when compared to those of a single-mode Brillouin laser with a single first-order Stokes component. Our experimental results are in excellent agreement with our numerical simulations, obtained thanks to our non-linear system describing the operation of a multi-Stokes Brillouin laser. This good match is mainly due to our ability: to obtain very precise values of the cavity parameters and the Brillouin gain coefficient using the CRDM technique ; to achieve long-term stability (hours); to finely control the detuning between the laser Stokes resonance and the frequency of the Brillouin gain maximum. We demonstrate experimentally for the first time that frequency noise is degraded in the presence of anti-Stokes Brillouin scattering. We also show that a gain detuning of the order of a few hundred kHz can degrade the intensity noise reduction or also increase the linewidth by amplitude-phase coupling. All these very fine observations thus allow us to set the fundamental limits of such laser systems such as: the increase in noise due to anti-Stokes orders; the role of pump noise and its possible interrelation with cavity finesse; the effect of the detuning inherent to higher Stokes orders. All these conclusions are key to the design and engineering of these Brillouin fiber lasers, which are currently attracting a great deal of interest as evidenced by the work in progress in the scientific community. This PhD thesis contributes to a better understanding of multi-Stokes Brillouin lasers

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LORENZI, ROBERTO. « Silica based functional materials : - Charge transport in nanostructured SnO2 : SiO2 thin films. - Second harmonic generation in niobium potassium silicate glasses. - Tapered silica optical microfibres for gas sensors ». Doctoral thesis, Università degli Studi di Milano-Bicocca, 2010. http://hdl.handle.net/10281/10933.

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"Charge transport in nanostructured SnO2:SiO2 thin films": Silica based nanostructured thin films grown on silicon substrates are promising materials for novel light emitter devices. In particular, tin dioxide is a wide band gap n-type semiconductor (Eg=3.6 eV) with an expected band-to-band emission centered in the ultraviolet (344 nm) region of the electromagnetic spectrum. Our group succesfully demonstrated UV emission from such systems, but at the beginning of my work many issues in charge transport processes needed to be explained. Aim of this project was to clarify electric transport and charge trapping mechanisms. As a result of a materials science approach we can now interpret the experimental data through specific relationships between synthesis conditions, clustering morphology (nanoparticle (NP) size distribution and volumic concetration, interphase substoichiometry, film thickness), and electric response. The observed phenomena have been analyzed within the percolation theory. Main results concern: electric transport of both holes and electrons is sustained by NP-to-NP hopping events and dielectric enhancement results from oscillating charges (holes) on NPs. "Second Harmonic Generation in potassium niobium silicate glasses": Second harmonic generation (SHG) is a non linear optical process largely employed in current laser technology and photonics. However in almost every application the material employed for these purposes are single crystals. Therefore the possibility to achieve large SHG in amorphous systems may lead to devices with innovative configurations. SHG may occur only if the system is non-centrosymmetric, therefore for glasses it is forbidden due to intrinsic isotropy. The inversion symmetry can be broken up with poling treatments. They consist in applying strong electrostatic field while the sample is stressed by external perturbation (typically heat, electron beam or laser light). We have explored the effect of thermal poling treatment on potassium niobium silicate glasses on inducing non linear optical properties. The results have revealed a strong SHG associated with structural modifications. The proposed mechanism involves a rearrangement of niobium oxide groups mediated by non bridging oxygen and potassium ion transport across the glass. These new charge arrangements form a non-centrosymmetric region underneath the anodic contact responsible of the detected SH signal. "Tapered silica optical microfibres for gas sensors": In the last years, tapered silica fibres have attracted much interest in photonic research, because of peculiar properties emerging in waveguides with lateral dimensions of the same order of the guided modes. In particular, in these structures the large evanescent field enables some interesting properties, such as microfluidic sensors and high Q optical resonators (coiling the tapered fibre), non-linear effects and supercontinuum generation. In this project, carried out at the University of Southampton (UK) in the group of Dr. Gilberto Brambilla, we have explored the feasibility of an innovative optical absorption device, based on ring down spectroscopy. In this case we are interested in a sensor for in-line application: a fluidic channel wrapped with tapered fibre in which the analyte can flow. The large power fraction outside the fibre interacts with the flowing medium and any change in the surrounding optical properties (refractive index or absorption coefficient) leads to a modification of the recorded light intensity propagating in the fibre. The idea is to exploit ring down time of a silica tapered microcoil resonator as an indicator of the absorption coefficient of a gas (or a liquid) flowing in the channel.

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Bescherer-Nachtmann, Klaus. « Fibre-Loop Ring-Down Spectroscopy Using Liquid Core Waveguides ». Thesis, 2013. http://hdl.handle.net/1974/7906.

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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

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Chen, Shun-Yi, et 陳順義. « Photodissociation of diiodomethane by using cavity ring down spectroscopy ». Thesis, 2010. http://ndltd.ncl.edu.tw/handle/55456166920337247451.

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碩士
國立臺灣大學
化學研究所
98
Cavity ring-down spectroscopy (CRDS) is a relatively new and quite sensitive technique for the measurement of gas phase. It holds the potential for simple, direct and sensitive measurement of the concentrations of a variety of trace gases in the atmosphere. In this thesis, We used CRDS to detect I2 produced from photodissociation of CH2I2. We can confirm this primary dissociation channel by energy dependence and pressure dependence experiments. The vibrational population ratio was found to be v0:v1:v2=1:0.65±0.1:0.3±0.05 .The quantum yield for the I2 elimination reaction is determined to be 0.004±0.002. We propose I2 elimination may process through the electronic ground state by internal conversion. This hypothesis is supported by the result of temperature dependence experiment. Moreover, the results agree with a given theoretical calculation.

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Chuang, Wan Ting, et 莊琬婷. « Photodissociation of CHBr3 studied by cavity-ring down spectroscopy ». Thesis, 2003. http://ndltd.ncl.edu.tw/handle/89488577426504957608.

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碩士
國立臺灣大學
化學研究所
91
Although the concentration of bromine in the stratosphere is less than that of chlorine, bromine is more effective at catalytically destroying ozone. Bromine atoms are roughly 100 times more effective at decomposing ozone than chlorine atoms. The photodissociation of bromine — containing molecules, therefore, are studied popularly recently. Cavity ring-down Spectroscopy (CRDS) is a relatively new direct absorption technique and its applications are developed very quickly in recent 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. Several advantages are inherent in CRDS. The technique doesn’t rely on fluctuations of the laser pulse. The effective absorption path length can be very long, such that it can be used in trace detection. The absorption is measured on an absolute scale. Another attractive property is the simplicity of its experimental setup. This thesis contains two major subjects; one is the absorption spectra of Br2 and I2, including electronic bound — free and bound — bound transition spectra. The other is the study of photodissociation of CHBr3. The visible, near UV absorption spectrum of Br2 involves transitions from the ground X1Σg+ state to three excited valence states ― A(3Π1u), B(3Π0+u), and C(1Π1u). In the case of Br2, A, B and C states are all strongly repulsive in the Franck — Condon region for absorption at ~ 500 nm. We attempt to determine the individual contributions of A, B, and C states to the continuum absorption. We also measure the absorption spectra of B 3Π0+u←X 1Σg+ (~500 nm) and A 3Π1u←X 1Σg+ (~700 nm) bound — bound transition of Br2. In the case of I2, the continuum absorption at ~500 nm is contributed from B and C states and ~ 700 nm is contributed from A state only. We also measure the absorption spectrum of B 3Π0+u←X 1Σg+ (~500 nm) bound — bound transition of I2. As for photodissociation studies of CHBr3, the major dissociation channel is found to be CHBr3 → CHBr2 + Br ΔH = 258 kJ/mol. In this work, we observed another channel, CHBr3 → CHBr + Br2 ΔH = 349 kJ/mol. We use two laser systems: one for the photolysis of CHBr3 and the other for the detection of the Br2 fragment by CRDS via B 3Π0+u ← X 1Σg+ bound — bound transition. A pulse/delay generator was used to vary the delay time between the photolysing and the probe lasers. We observed the nascent Br2 product distribution and calculated the vibrational and rotational energy from the absorption spectra of transition v” = 0 → v’ = 31 and v” = 1 → v’ = 41. According to the internal energy estimate, we attempted to interpret the photodissociation mechanism of CHBr3 to produce Br2. We also calculated the quantum yield of Br2.

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Chen, Bo-Jung, et 陳柏仲. « Photodissociation of Thionyl Chloride by Using Cavity Ring-Down Spectroscopy ». Thesis, 2014. http://ndltd.ncl.edu.tw/handle/81799547899976281921.

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