Thèses sur le sujet « Optical ring cavity »

The optical ring cavity has been studied for about ten years, both theoretically and experimentally. In these studies the uniform plane wave approximation has been used. In this work we investigate effects which result from the retention of the transverse diffraction. We establish that transverse structure is inevitable since plane wave fixed points are susceptible to transverse instabilities (modulational instability). We show that this instability is a universal mechanism for initiating various interesting and complicated, yet understandable, dynamical responses in a one and a two transverse dimensional cavity.

This thesis focuses on the construction and development of an experiment to study cold potassium atoms in an optical ring cavity. Firstly we load a potassium-39 magneto optical trap (MOT) inside the ring cavity. To achieve this a laser system, rectangular magnetic coils system and vacuum system are designed and constructed. To stabilise the laser system, a detailed study of various potassium spectroscopy techniques is undertaken and the reference laser is suitably locked to the magnetically induced spectroscopy. We load an ensemble of 10\(^5\) potassium atoms inside the ring cavity mode and study their collective strong coupling with the cavity field. In the collective strong coupling regime, the photons are coherently exchanged between the atomic ensemble and cavity field. This rate of exchange is determined by the singlephoton Rabi frequency `2\(g\)' which must be larger than the cavity field decay rate `2\(k\)' and atomic spontaneous emission rate `2\(ᵧ\)'. As a result of this coupling, the peak in the cavity transmission signal undergoes a splitting known as `vacuum Rabi splitting' (or `normal mode splitting'). The vacuum Rabi splitting has been realised and measured to be ~ 2\(π\). 18 MHz in our system.

Augmenting the level of integration for a lower cost and enhancing the performance of the optical devices have turned out to be the focus of many research studies in the last few decades. Many distinct approaches have been proposed in a significant number of researches in order to meet these demands. Optical planar waveguides stand as one of vital employed approach in many studies. Although, their low propagation loss, and low dispersion, they suffers from high power losses at sharp bends. For this reason, large radius of curvature is required in order to achieve high efficiency and compromise the high level of integration. For the purpose of this research, in this thesis different ways to improve the performance of optical microcavity ring resonators (MRRs) have been thoroughly investigated and new configurations have been proposed. The Multiresolution Time Domain (MRTD) technique was further developed and employed throughout this thesis as the main numerical modelling technique. The MRTD algorithm is used as a computer code. This code is developed and enhanced using self built Compaq Visual Fortran code. Creating the structure and Post-processing the obtained data is carried out using self built MATLAB code. The truncating layers used to surround the computational domain were Uniaxial Perfectly Matched Layers (UPML). The accuracy of this approach is demonstrated via the excellent agreement between the results obtained in literature using FDTD method and the results of MRTD. This thesis has focused on showing numerical efficiency of MRTD where the mesh size allowed or the total number of computed points is about half that used with FDTD. Furthermore, the MRR geometry parameters such as coupling gap size, microring radius of curvature, and waveguide width have been thoroughly studied in order to predict and optimise the device performance. This thesis also presents the model analysis results of a parallel-cascaded double-microcavity ring resonator (PDMRR). The analysis is mainly focus on the extraction of the resonant modes where the effect of different parameters of the structure on transmitted and coupled power is investigated. Also, accurate analysis of 2D coupled microcavity ring resonator based on slotted waveguides (SMRR) has been thoroughly carried out for the purpose of designing optical waveguide delay lines based on slotted ring resonator (SCROW). The SCROW presented in this thesis are newly designed to function according to the variation of the resonance coupling efficiency of a slotted ring resonators embedded between two parallel waveguides. The slot of the structures is filled with SiO2 and Air that cause the coupling efficiency to vary which in turn control both the group velocity and delay time of SCROW structures results from the changing the properties of the bent slotted waveguide modes which strongly depends on the slot’s position. Significant improvements on the quality factor and greater delay time have been achieved by introducing sub-wavelength-low-index slot into conventional waveguide.

This thesis describes an experiment which studies a cloud of magneto-optically trapped potassium-39 atoms inside an optical ring cavity. The potassium atoms are firstly cooled in a two-dimensional magneto-optical trap (MOT) and are then transferred into a three dimensional MOT which overlaps with the cavity mode. In this thesis, the optimisation of the MOT systems and the characterisation and construction of the optical ring cavity are discussed. After exploring these two systems independently, the two systems are then coupled together to provide an atom-cavity system, which exhibits collective strong coupling. The system is shown to exhibit normal-mode splitting, with a collective Rabi splitting of G = 2π (6.25±0.50)MHz, corresponding to (4.7±0.6) x 103 atoms in the cavity. Whilst collective strong coupling has been achieved before in other experiments, we believe this is the first experiment to achieve this with potassium. The next goal in the experiment is to control the group refractive index of the atoms inside the cavity. The modification of the group index using electromagnetically-induced transparency (EIT) on hot atoms inside a vapour cell has already been previously demonstrated by this experiment; and using the same laser system we aim to demonstrate EIT on the cold intra-cavity atoms as well. Gain mechanisms could also be used to create a ring laser with a controllable group index. These techniques could lead to a range of applications such as enhanced-sensitivity laser ring gyroscopes and active optical clocks.

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.

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.

A Nephelometry camera (NephCam) and Humidity Controlled Cavity Ring-Down Transmissometer (HC-CRDT) were developed for the determination of aerosol optical properties. The NephCams use a reciprocal geometry relative to an integrating nephelometer; a diode laser illuminates a scattering volume orthogonal to a charge coupled device (CCD). The use of a CCD allows for measurement of aerosol scattering in 2 dimensions; scattering coefficients and size information can be extracted. The NephCam's optics were characterized during a set of imaging experiments to optimize the images collected by the camera. An aperture setting of 1.6 was chosen because it allowed for the most light intensity to reach the CCD - albeit with significant vignetting - and also had a constant modular transfer function (MTF) across the image; approximately 0.3. While this MTF value is approaching the minimum usable MTF of 0.2, other aperture settings did not exhibit constant MTF. While the effects of vignetting can be corrected in image post processing, the effects of non-constant MTF cannot. An optical response model was constructed to simulate images collected by the NephCams as a function of particle type and size. Good agreement between modeled and measured images was observed after the effects of contrast on image shape were considered. The image shapes generated by the model also pointed towards the use of polynomial calibration for particle sizes less than 400 nm as a result of multiple charge-to-size effects present from the sizing mechanism of the differential mobility analyzer. Initial calibration of the NephCams using size-selected dry Ammonium sulfate (AS) showed that calibration slopes are a function of particle size which is also in agreement with the model. Calibration slopes decreased as particle size increased to 400 nm; after 400 nm calibration slope oscillated around a common value. This effect is directly related to the forward shift of scattered intensity as particles grow in size and the collection efficiency of the NephCam as particle size increases. The single scattering albedo (SSA) of Nigrosin was calculated using the NephCam; extinction was measured by the HC-CRDT. Good agreement between the SSA and size was noticed for larger particle sizes; particles smaller than 200 nm in diameter over-measured the SSA of Nigrosin because of the multiple charge-to-size effect. In this size regime, light scattering by particles increases much more quickly than absorption; the presence of larger particles causes scattering to be artificially high. The HC-CRDT is a 4 channel, 3 wavelength instrument capable of measuring the extinction coefficients of aerosols at high (> 80%), low (< 10%) and ambient relative humidity. Extinction coefficients as a function of RH were determined for AS, NaNO3, NaCl, and Nigrosin; these particles represent surrogates of the strongly scattering ionic salts and black carbon, respectively. A model was developed to calculate the changes in refractive index and extinction coefficients of these water soluble particles as a function of RH; these particle types were chosen because core-shell morphologies could be avoided. Volume mixing, Maxwell-Garnett and partial molar refraction mixing rules were used to calculate effective refractive indices as a function of water uptake. Particle growth was calculated based upon the Kelvin equation. Measured and modeled results of f(RH) - relative change in extinction between high or ambient RH and dry RH - agree well for all particle types except Nigrosin. This disagreement is thought to stem directly from an incomplete parameter set for Nigrosin; growth parameters were assumed to be identical to NaNO3, density assumed to be 1 g/mL and molecular weight 202 g/mole, which may not be true in reality (different suppliers of Nigrosin quote different molecular weights). The NephCam was not used during these experiments, so the addition of a scattering measurement to better characterize the growth by Nigrosin is necessary. The f(RH) data for NaNO3 showed excellent agreement between measured and modeled data; however particle size information collected by an SMPS does not agree with the theory. This stems from the fact that NaNO3 does not show prompt deliquescence upon drying; instead an amorphous solid forms which exhibits a kinetically limited loss of water.

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

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.

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

In the first chapter, a Q-switched fiber laser that is capable of generating transform-limited pulses based on single-frequency fiber laser seeded ring cavity is demonstrated. The output pulse width can be tuned from hundreds of nanoseconds to several microseconds. This Q-switched ring cavity fiber laser can operate over the whole C-band. In addition, a theoretical model is developed to numerically study the pulse characteristics, and the numerical results are in good agreements with the experimental results. In the next chapter, a Raman fiber laser is developed for generating signal at 1480 nm. Initial experimental results has demonstrated generating of Raman laser at 1175 nm, 1240 nm, 1315 nm, and 1395 nm wavelength. Finally, a free space fiber amplifier is studied both theoretically and experimentally. The experimental work has demonstrated signal coupling efficiency up to 90% in the NP highly Er/Yb co-doped phosphate fiber.

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

Dispositivos fotônicos têm estado continuamente no foco das pesquisas científicas, particularmente em aplicações para comunicações ópticas e sensoriamento. Por outro lado, as dimensões desses dispositivos são restringidas pelo limite de difração de Abbe. Esse limite tem se mostrado como o grande gargalo no desenvolvimento de novas tecnologias em microscopia óptica, litografia de projeção óptica, óptica integrada, e armazenamento óptico de dados, por limitar as dimensões e a capacidade de integração destes dispositivos. Felizmente, a \"plasmônica\" surgiu como um novo campo de estudo, possibilitando a superação dessa limitação por meio da propagação da luz em modos de plasmon-poláritons de superfície - SPP (Surface Plasmon Polariton). De maneira simplificada, SPPs são campos eletromagnéticos confinados em regiões menores que o comprimento de onda da luz. A geração de SPP ocorre por meio da excitação coletiva de elétrons na interface entre dois meios, metal-dielétrico, que se acoplam com a onda eletromagnética incidente. Pesquisadores logo perceberam que guias de onda baseados em SPP poderiam transportar a mesma banda de informação que um dispositivo fotônico convencional e serem tão localizados quanto dispositivos eletrônicos (elétrons têm maior capacidade de confinamento que fótons). Dessa maneira, alterando a estrutura da superfície de um metal, as propriedades dos SPPs - em particular sua interação com a luz - podem ser manipuladas, oferecendo potencial para o desenvolvimento de novos tipos de dispositivos fotônicos. Com isso, nanoestruturas capazes de guiar, dividir ou mesmo sintonizar a luz tornaram-se realidade. No presente trabalho, o fenômeno de geração de SPPs é estudado teoricamente e aplicado na modelagem de diversas estruturas de interesse científico e tecnológico, tais como filtros de cavidade ressonante e ressoadores em anel. O objetivo principal é a obtenção de estruturas capazes de filtrar ou sintonizar comprimentos de onda, minimizando as perdas ao máximo. Com isso, espera-se estender e explorar ainda mais o leque de possíveis aplicações.
Photonic devices have continuously been in the focus of scientific research, particularly for optical communications and sensing applications. On the other hand, the dimensions of these devices are well known to be limited by the Abbe\'s diffraction limit. This limit has been the major bottleneck in developing new technologies in optical microscopy, lithography projection optics, integrated optics, and optical data storage, as it limits the size and ability to integrate these devices. Fortunately, the field of \"Plasmonics\" has emerged and devices whose dimensions overcome the difraction limit have now become reality. This is possible with the propagation of light in the form of Surface Plasmon Polariton - SPP that, in a simplified way, is an electromagnetic field confined in regions smaller than the wavelength of light. SPP occurs via collective excitation of electrons at the interface between two media, metal-dielectric, as a result of the coupling with an incident electromagnetic wave. Researchers soon realized that waveguides based on SPP could carry the same band of information as that of a conventional photonic device and yet be as localized as electronic devices (electrons have a greater capacity for confinement than photons). Thus, changing the structure of the surface of a metal, the properties of SPPs - in particular its interaction with light - can be manipulated, offering potential for the development of new types of photonic devices. Thus, nanostructures capable of transferring, guiding, splitting, or even tuning the light have now become reality. In this work, the phenomenon of generation of SPPs is theoretically investigated and applied to various structures of scientific and technological interest, such as filters and cavity resonators. The main objective is to obtain structures that are able to filter or tune wavelengths, minimizing losses as much as possible. As a result, we expect to extend and explore even further the range of possible applications.

La technologie optique integree sur substrat silicium permet la realisation d'un microguide d'ondes en anneau couple a des microguides rectilignes formant ainsi une cavite resonante. Cette etude apporte des solutions theoriques et de premiers resultats experimentaux pour cet interferometre integre. Une presentation des resonances observables par interferences a ondes multiples est donnee puis l'influence des divers parametres sur les pics de resonance est etudiee. Une evaluation des pertes dues a la courbure de ces microguides est effectuee et le couplage entre microguides est calcule par la methode de perturbation. Les parametres technologiques utilisables sont ensuite determines pour differents rayons d'anneau et les caracteristiques de resonance des anneaux realises sont indiquees ainsi que les valeurs de pertes et de couplage qui s'en deduisent

Linear tuning the frequency of an erbium-doped fiber ring laser using both a Fabry-Perot filter and an electro-optic tunable filter has been experimentally demonstrated. The rate of frequency change is determined by monitoring the fringes produced by laser light transmitted through a fiber Fabry-Perot interferometer. The fiber ring laser has been tuned over a 50 nm spectral range when using the Fabry-Perot filter and a tuning rate of 16480 nm/s has been achieved. The spectral width of the laser is 0.049 nm and the nearest sidelobe to the main peak is more than 30 dB below the central lobe. When the electro-optic tunable filter is used, a spectral range of 11 nm is reached. The spectral width is 2.33 nm and is in close agreement with the filter theoretical results. The sidelobe to main peak difference is around 13 dB.

A ring laser gyroscope is a device which employs a ring laser to measure rotation. A ring laser supports two beams propagating in opposite directions around the ring resonator. When the gyroscope is rotated, the frequencies of the two beams split by an amount proportional to the rate of rotation: the device works by measuring this frequency splitting. The main problem of ring laser gyroscope design is the frequency synchronisation - lock-in - of the two beams at low rates of rotation. Lock-in arises from weak mutual coupling caused by backscattering at the mirrors and results in a dead band around zero. One of the possible solutions to this problem is a two-mode ring laser in which two modes oscillate simultaneously and interact to reduce the dead band. The present work reviews the theory of lock-in and offers a theoretical basis for this approach, as well as providing experimental evidence to support it.

碩士
國立臺灣師範大學
光電科技研究所
95
In this thesis, we integrated development of optical waveguide for the active and the passive device has become the future trend. We propose optical waveguide components for optical micro-ring resonator building on silicon-on-insulator (SOI) wafers, and also integrated air-bridge structure and the simulation is based on the well-known Finite-difference Time Domain (FDTD) technique. We used the free-carrier plasma dispersion effect and Schottky diode structure to modulate our filter and optical switch device; we devote our attraction on the electro-optical micro-ring resonator to apply in optical communication system. In sensing applications, we also design the geometric structure of resonance cavity to see different resonances are discussed in the thesis. We design the micro-ring their have small size, low cost, and potential for high sensitivity make them attractive for bio-sensing applications.

碩士
國立中山大學
光電工程研究所
95
The goal of the thesis is to fabricate the integrated asymmetric Mach-Zehnder Interferometer and optical waveguide ring resonator with simple fabrication process. 1.41μm and 1.49μm symmetric quantum well InGaAlAs epitaxial wafer is used to fabricate the devices. In the asymmetric Mach-Zehnder Interferometer , we design asymmetric straight waveguides with difference optical path differences ΔL=480μm, 970μm, and 1900μm. And asymmetric bend waveguides with curvature radius differences ΔR=260μm, 200μm, 160μm, and 100μm. By this design, we can observe the interference variation of output light. In optical waveguide ring resonator design, we reduce the length of original K=0.15 Multi-Mode Interference (MMI) by stepped-width waveguide. By three-stepped width waveguide MMI design, it can be reduced 33.2% length. We obtain different transmission spectrum by adjusting the splitting ratio of MMI couplers (K=0.85, 0.5, and 0.15) and cascading doudle rings. We use a series of two ring resonators by MMI (K0=0.5,K1=0.15,K2=0.5) to get the FSR=50GHz. In fabrication process, we combined dry etching method with RIE-ICP and wet etching to get smooth sidewall and highly vertical waveguide. In measure , we get the FSR= 41.25 GHZ in throughput port in double ring filters . No signal in drop port was obserred due to material absorption, bending loss, and waveguide loss.

碩士
國立中山大學
光電工程研究所
95
In this thesis, we have established an optical measurement system to measure the device characteristics. We focus on the investigation of semiconductor optical amplifier, Fabry-Perot laser, and ring cavity filter. We used InP-based multiple quantum wells epitaxial wafer with modulation doping in the active layer. A 1.41 μm symmetric InGaAlAs/InP quantum well structure is used to fabricate the optical waveguide ring resonator devices for the optical communication region at 1.55μm wavelength. For the semiconductor optical amplifier and lasers, we designed two different types: Fabry-Perot Amplifier (FPA), and Traveling Wave Amplifier (TWA). The InGaAlAs-FPA structure has three lasing peaks at 1514 nm, 1528 nm, and 1544 nm. The InGaAlAs-TWA-a structure has only one peak at 1510 nm. The InGaAsP-TWA-b structure has a gross gain = 8.5 dB (wavelength = 1575 nm) at pumping current = 22 mA. We used Hakki-Paoli method and transparency current to calculate gain spectrum. For ring cavity filter, the optical spectrum has a FSR = 41.25 GHz.

博士
國立中山大學
光電工程研究所
95
In this study, we propose and demonstrate a flat-top birefringent optical interleavers utilizing a new ring-cavity as a phase-shift element. The uniform performance over entire C-band is a result of the unique ring-cavity architecture which utilizes Fresnel reflections of the prism-air interface to provide the partial reflections. Unlike dielectric mirrors with thin-film coatings, the reflectivities of Fresnel reflection are insensitive to wavelength variations in the transmission band. In the ring-cavity based birefringent interferometer (RCBI) interleaver, the spectral transmission characteristics of the interleaver with a 25-GHz channel spacing exhibits a 0.5-dB passband larger than 17.5 GHz (70% of the channel spacing), a 25-dB stopband greater than 17.5 GHz (70% of the channel spacing), a channel isolation better than 28 dB, and insertion loss lower than 2.2 dB. In the ring-cavity based birefringent Sagnac interferometer (RCBSI) interleaver, the spectral transmission characteristics of the interleaver with a 25-GHz channel spacing exhibits a 0.5-dB passband larger than 18.1 GHz (72.5% of the channel spacing), a 25-dB stopband greater than 18.1 GHz (72.5% of the channel spacing), a channel isolation better than 36 dB, and insertion loss lower than 1.5 dB. The RCBSI interleaver requires less number of optical components and hence results in more than 0.7 dB and 2.5% improvements in the insertion loss and band utilization, respectively, when compared to the RCBI interleaver. Therefore, the novel RCBSI interleaver can be used in dense wavelength division multiplexing (DWDM) applications.

Over the last three decades, atom interferometry has been developed rapidly and has become an important tool in quantum metrology. It has been widely applied both in the test of fundamental physics and in the precise measurement of gravity and gravity gradients. Atom interferometers based on the alkaline-earth (like) atoms such as strontium (Sr) and ytterbium (Yb) have attracted increasing attention due to the existence of narrow intercombination transitions and ultra-narrow clock transitions. The bosonic 88Sr is a good candidate for transportable and space-borne atom interferometers due to the immunity to stray magnetic fields in its electronic ground state, long coherence time and low collision rate. It can therefore be used in space projects for precision measurement of gravity and gravity gradients. However, there is a fundamental limit to the precision in a phase shift measurement with atom interferometers, which is set by the number of atoms involved. This limit is known as the standard quantum limit. It is possible to surpass this limit by introducing correlations in the atomic ensembles thus reducing the phase uncertainty at the expense of an increase in the population uncertainty. In this case the spin-squeezed states are generated and can be used to improve the phase resolution of atom interferometers. In this thesis, a method to generate spin squeezed states in 88Sr momentum states for atom interferometry is considered and the necessary technology that allows its implementation will be presented. Spin squeezing is achieved by resolving the Doppler effect due to momentum state superposition via cavity- enhanced nondestructive measurement. An optical ring cavity is designed and constructed for quantum nondestructive measurements. However, one major obstacle that blocks the way to spin squeezing via cavity-enhanced measurement arises from cavity length fluctuations, which can totally mask the atomic signal if no appropriate scheme is adopted. Therefore, a method to cancel the cavity length fluctuations in measuring the atom-induced phase shift is proposed and close to 30 dB reduction of the cavity noise down to the noise floor has been demonstrated. We further apply the demonstrated noise-reduced measurement scheme in the simulated squeezing experiment, where we mimic the atom-induced cavity phase shift by varying the frequency of one of the two circulating beams. The noise cancellation scheme demonstrates an improvement of a factor of 40 in phase sensitivity with a phase resolution of 0.7 mrad. With this improvement we estimate that the cavity noise will no longer play an important role in a real spin squeezing measurement.

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

Precise measurements of both absolute frequencies and small frequency differences of atomic energy levels have played an important role in the development of physics. For example, high precision measurements of absolute frequencies of the 2S½ → 2P ½ transition (D1 line) of alkali atoms form an important link in the measurement of the fine structure constant, α. Similarly, precise interferometric measurements of the local gravitational acceleration (g) rely on the knowledge of the absolute frequencies of the 2S½ → 2P 3/2 transition (D2line) in alkali atoms. Difference frequency measurements of hyperfine structure and isotope shifts of atomic energy levels provide valuable information about the structure of the nucleus, which in turn helps in fine tuning the atomic wave functions used in theoretical calculations. The work reported in this thesis starts with the development and refinement of high precision measurement of absolute frequencies using a ring-cavity resonator. The measurement technique is relatively simple and cost-effective, but the accuracy is comparable to that achieved with the frequency comb technique (10¯11) when the accuracy is limited by the natural linewidth of the transition being measured. The technique combines the advantages of using tunable diode lasers to access atomic transitions with the fact that the absolute frequency of the D2 line in87Rb is known with an accuracy of 6 kHz. A frequency-stabilized diode laser locked to this line is used as a frequency reference, along with a ring-cavity resonator whose length is locked to the reference laser. For a given cavity length, an unknown laser locked to an atomic transition has a small frequency offset from the nearest cavity resonance. We use an acousto-optic modulator (AOM) to compensate for this frequency offset. The measured offset is combined with the cavity mode number to obtain a precise value for the frequency of The unknown laser. We have used this technique for absolute frequency measurements Of the D lines in133Cs and 6,7Li, and the 398.8nm line in Yb. We have also developed a technique to measure the ‘difference frequency’ of atomic energy levels using a single diode laser and an AOM. In this technique, the laser is first locked to a given hyperfine transition. The laser frequency is then shifted using the AOM to another hyperfine transition and the AOM frequency is locked to this difference. Thus the AOM frequency directly gives a measurement of the hyperfine interval. Applying this AOM technique we have measured the hyperfine interval of the D1 lines of all alkali atoms with high precision. We have further developed a technique of coheren-tcontrol spectroscopy (CCS) using co-propagating control and probe beam that is useful for highresolution spectroscopy. In this technique, the probe beam is locked to a transition and its absorption signal is monitored while the control beam is scanned through neighbouring transition. As the control comes into resonance with another transition, the probe absorption is reduced and the signal shows a Doppler free dip. This technique allows us to resolve transitions that are otherwise swamped by crossover resonances in conventional saturated absorption spectroscopy (SAS). We have applied this technique to measure hyperfine intervals in the D2 line of several alkali atoms. Thus, we were able to do high-precision measurements of both absolute and difference frequency of atomic transitions. The precision of the absolute frequency measurement is finally limited by the accuracy of 6 kHz with which the reference frequency is known. The nearby two photon transition in Rb, i.e. the 5S1/2→5D3/2 transition at 778 nm, is known with an accuracy of 1 kHz. In future, we hope to improve the accuracy of our technique using this transition as the reference. This thesis is organized as follows: In Chapter1,we give a brief introduction to our work.. We review the importance of frequency measurements and precision spectroscopy, followed by a comparison of the frequency comb and our ring cavity technique. In Chapter2, we describe measurements of the absolute frequency of the D lines of 133Cs using the ring cavity. We give a detailed discussion of the technique, the Possible sources of errors, and ways to check for the errors. The measurement of the absolute frequency of the D lines of Cs allows a direct comparison to frequency comb measurements, and thus acts as a good check on our technique. In Chapter 3, we describe the absolute frequency and isotope shift measurements in the 398.8 nm line in Yb. We probed this line by frequency doubling the output of a tunable Ti:Sapphire laser. We obtained< 60 kHz precision in our measurements and were able to resolve several discrepancies in previous measurements on this line. In Chapter 4, we describe the measurement of hyperfine structure in the D1 lines of alkali atoms. We used conventional saturated-absorption spectroscopy in a vapor cell to probe different hyperfine transitions and then used our AOM technique to measure the hyperfine interval with high precision. In Chapter 5 we discuss our measurements of hyperfine structure in the D2 lines of several alkali atoms. In the case of 23Na and 39K, the closely-spaced hyperfine transitions are not completely resolved in conventional saturatedabsorption spectroscopy due to the presence of cross over resonances. We have used coherent control spectroscopy to obtain crossover-free spectra and then measured the hyperfine intervals using an AOM. This technique was also used for high resolution spectroscopy in the D2 line of 133Cs. Finally, we describe our measurements of hyperfine structure in the D2 line of Rb using normal saturated absorption spectroscopy. Chapter 6, describes the relative and absolute frequency measurements in the D lines of6,7 Li at 670nm. High-precision measurements in lithium are of special interest because theoretical calculations of atomic properties in this simple three electron system are fairly advanced. Lithium spectroscopy poses an experimental challenge and we describe our efforts in doing highresolution spectroscopy on this system. Chapter 7 describes the hyperfine spectroscopy on the1P 1 state of 173Yb. Measurement of hyperfine structure in 173Yb has a problem because two of the hyperfine transitions overlap with the transition in 172Yb. In our earlier work (described in chapter 4), we had solved this problem by using multipeak fitting to the partially resolved spectrum. Here, we directly resolve the hyperfine transitions by using transverse laser cooling to selectively deflect the 173Yb isotope. In Chapter 8 , we give a broad conclusion to the work reported in this thesis and suggest future avenues of research to continue the work commenced here.

This thesis studies frequency-shifted interferometry (FSI), a useful and versatile technique for fiber-optic sensing. I first present FSI theory by describing practical FSI configurations and discussing the parameters that affect system performance. Then, I demonstrate the capabilities of FSI in fiber-optic sensor multiplexing and high sensitivity chemical analysis. We implemented a cryogenic liquid level sensing system in which an array of 3 fiber Bragg grating (FBG) based sensors was interrogated by FSI. Despite sensors' spectral overlap, FSI is able to separate sensor signals according to their spatial locations and to measure their spectra, from which whether a sensor is in liquid or air can be unambiguously determined. I showed that a broadband source paired with a fast tunable filter can be used in FSI systems as the light source. An array of 9 spectrally overlapping FBGs was successfully measured by such a system, indicating the potential of system cost reduction as well as measurement speed improvement. I invented the the FSI-CRD technique, a highly sensitive FSI-based fiber cavity ring-down (CRD) method capable of deducing minuscule loss change in a fiber cavity from the intensity decay rate of continuous-wave light circulating in the cavity. As a proof-of-principle experiment, I successfully measured the fiber bend loss introduced in the fiber cavity with FSI-CRD, which was found to be 0.172 dB/m at a bend radius of 12.5 mm. We then applied FSI-CRD to evanescent-field sensing. We incorporated fiber tapers as the sensor head in the system and measured the concentration of 1-octyne solutions. A minimum detectable 1-octyne concentration of 0.29% was achieved with measurement sensitivity of 0.0094 dB/% 1-octyne. The same system also accurately detected the concentration change of sodium chloride (NaCl) and glucose solutions. Refractive index sensitivity of 1 dB/RIU with a measurement error of 1*10^-4 dB was attined for NaCl solutions. Finally, I proposed a theoretical model to study the polarization effects in FSI systems. Preliminary results show that the model can already explain the experimental observations. It not only provides insight into how to improve system performance but also suggests potential new applications of the technique.

The quality of machinery liquids plays a critical role in ensuring safe and cost-effective operation of engines. Especially in the aviation industry, there is a great need for real-time and online monitoring of the purity, lubricity and age of machinery fluids. In this work, two optical techniques, excitation-emission matrix spectroscopy (EEMS) and cavity ring-down spectroscopy (CRDS), are used for monitoring of degradation and contamination of aero-turbine lubricants and jet fuels using optical fiber probes. We implement EEMS combined with a modified fiber probe design to characterize lubricant quality through the characteristic fluorescence of antioxidant additives. Multi-way analysis procedures, such as parallel factor analysis, are applied to correlate spectral features to antioxidant concentration, oxidative stability, and lubricant age. The spectroscopic data are then correlated to commonly used, off-line parameters such as the induction time and the breakdown number. It is shown that the decrease in fluorescence intensities of antioxidants coincides with the decomposition of the oil base stock. The induction times of synthetic jet turbine oil degraded at 150ºC, 195ºC and 215ºC are found to be at about 10,000, 3,500 and 400 min respectively. Simple kinetic models are developed that are capable of describing antioxidant reactions as pseudo first-order processes. We also demonstrate that with fluorescence detection it is possible to determine the concentration of oil contamination in jet fuel from about 10 to 1000 ppmv. In addition, a fiber-loop cavity ring-down spectrometer has been developed to quantitatively identify oil contamination of jet fuel by measuring optical absorption in the UV region. CRDS is a very sensitive, path-enhanced absorption technique that may be used for trace-species measurements in gas and liquids. The absorption measurements on samples with small volumes are characterized by measuring the concentration of turbine oil in jet fuel from 100 000 ppmv to a limit of detection of 400 ppmv. In summary, the obtained results permit us to specify the life time of lubrication oil and to determine the contamination of jet fuel with turbine oil qualitatively and quantitatively. In a simple optical configuration the fiber-coupled EEM and CRD methods permit in situ sampling of the machinery fluids.
Thesis (Ph.D, Chemistry) -- Queen's University, 2014-04-25 13:24:37.761

Le missioni spaziali per osservazione della Terra o per scopi scientifici richiedono giroscopi per la misurazione della velocità angolare con performance elevate (risoluzione nell’intervallo 0.1 – 1 °/h e stabilità della polarizzazione nell’intervallo 0.001 – 0.1 °/h) per un accurato controllo dell’ assetto e dell’orbita del satellite. Affidabilità, resistenza alle radiazioni, robustezza, tolleranza agli urti, volume ridotto e basso consumo energetico sono i requisiti tipici dei sensori di velocità angolare di nuova generazione per applicazioni spaziali. In tale contesto, i risonatori ad anello fotonici stanno emergendo come elementi chiave di sistemi con elevate performance e dimensioni compatte. In particolare, per testarne l’affidabilità in ambiente spaziale, è stata dimostrata sperimentalmente un’ elevata resistenza alle radiazioni di un risonatore ad anello in InP investito da radiazioni γ. Nella tesi sono state discusse le potenzialità di un risonatore ad anello con elevato fattore di qualità Q, che funge da elemento sensibile di un giroscopio ottico risonante (RMOG) miniaturizzato con performance elevate. L'elemento chiave del giroscopio proposto è un semplice risonatore ad anello basato su Si3N4 con un cristallo fotonico monodimensionale presente lungo l’intera circonferenza del risonatore ad anello, denominato 1D-PhCRR. Il funzionamento si basa sullo sfruttamento dell'effetto di luce lenta, tipico dei cristalli fotonici, che garantisce un miglioramento del fattore di qualità di oltre 3 ordini di grandezza rispetto ad un semplice risonatore ad anello con medesimo raggio. Un PhCRR con fattore di qualità > 109, è stato teoricamente dimostrato mediante l’utilizzo di un modello matematico basato sulla teoria dei modi accoppiati (CMT). Tali performance garantiscono una risoluzione teorica del giroscopio < 0.05 °/h con un volume ridotto (< 1 cm3), conforme ai requisiti degli operatori spaziali. Lo sviluppo del 1D-PhCRR è stato condotto nell'ambito del contratto NPI dell'Agenzia Spaziale Europea (ESA), che sponsorizza le attività di dottorato. Oltre a risultare idoneo come elemento sensibile nei sottosistemi di controllo di assetto e orbita, il PhCRR potrebbe essere utilizzato per implementare diverse funzionalità nei payload di futura generazione per telecomunicazioni o per l’ osservazione della Terra. Negli ultimi anni, un notevole interesse è stato rivolto verso payload per telecomunicazioni in grado di essere adattati ed ottimizzati dopo il lancio, secondo le diverse esigenze degli utenti in termini di larghezza di banda, area di interesse ed allocazione delle frequenze. La fotonica nel regime delle microonde risulta essere l’approccio più adatto per soddisfare i requisiti dei payload di futura generazione per telecomunicazioni. In tale contesto, è stato proposto un filtro notch basato su PhCRR in silicio con larghezza di banda B = 10.43 GHz ed extinction ratio ER > 40 dB, con risposta in frequenza con profilo gaussiano, ottenuta mediante inserimento ed ingegnerizzazione di difetti all’interno del cristallo fotonico. Implementando giunzioni p-i-n in corrispondenza dei difetti, è stato dimostrato un ampio intervallo di variazione della frequenza centrale di filtraggio (15 GHz), in un rapido tempo di commutazione (≈ 1 ns) ed un consumo di energia pari a 47 mW. Inoltre, è stata proposta l’architettura innovativa di un’ oscillatore optoelettronico miniaturizzato in banda Ka, basata sul PhCRR progettato. È stato calcolato teoricamente un rumore di fase a 10 kHz di offset dalla portante (40 GHz) pari a circa -155 dBc/Hz con potenza elettrica in uscita> 10 dBm. Tali performance rappresentano un notevole miglioramento rispetto agli oscillatori optoelettronici riportati allo stato dell'arte. L'elevata purezza del segnale oscillante è stata sfruttata per la progettazione di un generatore di segnale chirpato, utile per i sistemi SAR (radar ad apertura sintetica) ad alta risoluzione per l'osservazione della Terra, con un prodotto tempo-larghezza di banda di 3200 e un rumore di fase di circa -116 dBc/Hz. Per sistemi SAR, è stata progettata una linea di ritardo fotonica tunabile in banda X, basata su un cristallo fotonico realizzato mediante pattern di uno strato di grafene, in grado di garantire un elevato angolo di puntamento in fase di trasmissione del segnale e la più alta figura di merito riportata allo stato dell’ arte.
Science and Earth observation missions require high-class gyroscopes, having a resolution in the range 0.1 – 1 °/hr and a bias stability in the range 0.001 – 0.1 °/hr, for an accurate control of the satellite attitude and orbit. High reliability, high radiation resistance, high robustness, high shock tolerance, small volume, low power consumption and reduced mass are typical requirements of new generation angular rate sensors for Space applications. In this context, the photonic ring resonators are emerging as key building blocks. The radiation hardness of a ring resonator useful for Space applications has been investigated, demonstrating a negligible worsening of the performance under γ radiations. In this thesis, the potentiality of an ultra-high-Q ring resonator, acting as sensitive element of a resonant micro-optic gyroscope architecture (RMOG), has been discussed, aiming to design a chip-scale, high performing gyroscope. The key element of the proposed RMOG configuration is a Si3N4-based simple ring resonator with a one-dimensional photonic crystal included along the whole optical path, called as 1D-PhCRR. Its operation is based on the exploitment of the slow light effect, typical of the PhC, providing an improvement of the Q-factor respect a simple ring resonator more than 3 order of magnitude. The Si3N4 PhCRR with Q > 109, has been theoretically demonstrated by using a self-made mathematical model, based on the Coupled Mode Theory (CMT). This performance ensures a gyro resolution < 0.05 °/hr with a small volume (< 1 cm3), compliant to the Space operators’ requirements. The development of the 1D-PhCRR has been carried out in the framework of the European Space Agency NPI contract, that sponsor the PhD activities. Besides its suitability for attitude and orbit control sub-systems, the PhCRR could be used to implement several functionalities in the next photonic-based generation telecom payloads and for Earth observation purpose. Telecom satellites are the most mature Space applications. In the last decades, Space operators require flexible telecom payload that can be adapted and optimized after the launch, according to the varying user demands in terms of bandwidth, coverage, and frequency allocation. The microwave photonic represents the most suitable approach to fulfil the next-generations telecom payloads requirements. In this context, photonic-based microwave filters have been investigated, and the design of a silicon – based PhCRR with a bandwidth B = 10.43 GHz and ER > 40 dB, acts as notch filter, has been reported. By inserting and engineering defects into the PhC section, superimposed the PhC on a ring resonator section, a Gaussian-shaped frequency response, with very steep sidewalls, has been simulated. A continuous tuning of the filtering central frequency (15 GHz), with a fast switching time (≈ 1 ns) and power consumption of 47 mW is ensured, by exploiting the free carrier plasma dispersion effect in correspondence of PhC defects. Furthermore, the theoretical feasibility of a miniaturized Ka-band optoelectronic oscillator, based on the designed PhCRR, with a phase noise at 10 kHz offset from the carrier of about -155 dBc/Hz and an output electric power > 10 dBm has been demonstrated, that represent a remarkable improvement respect to the state-of-the-art. The high purity of the oscillating signal has been exploited for the design of a linearly chirped microwave generator, useful for high-resolution Synthetic Aperture Radar (SAR) systems for Earth Observation, with a time-bandwidth product of 3200 and a phase noise of about -116 dBc/Hz. The design of an ultra-compact graphene-based optical delay line useful for the beamsteering/beamforming in X-band, is reported to ensure a wide swath size of SAR systems, with high range resolution, simulating the highest figure of merit reported at the state-of-the-art.