[pt] Este trabalho visa estabelecer na prática a estatística do ganho dependente da polarização (PDG-Polarization Dependent Gain) em sistemas ópticos com amplificação Raman. A amplificação Raman depende fortemente da polarização relativa entre os fótons de bombeio e de sinal, que tem que ser paralelas para máximo ganho [1]. Portanto, a birrefringência é um importante limitador de desempenho de sistemas de longa distância amplificados por esta técnica visto que modifica os estados de polarização de forma diferente para cada comprimento de onda. A birrefringência varia aleatoriamente de acordo com as flutuações do ambiente onde está a fibra óptica, dando origem à dispersão dos modos de polarização, efeito este conhecido pela sigla PMD. Alguns experimentos recentes mostraram que o amplificador Raman não só depende do estado de polarização do sinal de entrada, mas também que o valor da dependência do ganho com a polarização (PDG- Polarization Dependent Gain) flutua devido a natureza aleatória da PMD [4,5]. É importante conhecer a estatística da PDG, sua relação com a PMD e como a PDG pode ser reduzida a níveis aceitáveis. Nesse trabalho será medida experimentalmente a distribuição estatística da PDG em fibras de dispersão deslocada e os resultados comparados com as previsões teóricas dadas por [2]. / [en] Raman amplifiers are very attractive because they provide a large and relatively flat gain over a wide bandwidth while maintaining a small noise figure, and they can be made using regular silica fiber. However, the Raman Gain coefficient is polarization sensitive and can be up to ten times higher when the signal and pump polarization states are parallel rather than perpendicular [1]. Usually fibers present some degree of residual asymmetry - because the fiber core is slightly out-of-round, or because of mechanical stress on the deployed fiber - and this causes polarization mode dispersion. The light traveling along one polarization axis moves slower or faster than the light polarized along the other axis. This effect distorts the signal and causes polarization fluctuations along the fiber. As the Raman gain is higher when the signal and pump polarization states are parallel these fluctuations of the relative polarization between signal and pump vary the instantaneous value of the Raman gain. So the Polarization Dependence Gain (PMG) is directly related to the PMD. Several experimental studies have shown not only that the gain of raman amplifiers depends on the state of polarization of the input signal but also that this polarization-dependent gain (PDG) fluctuates over a wide range because of the random nature of polarization mode dispersion (PMD) [4,5]. It is important to know the statistics of PDG, its relationship to the PMD, and how the PDG can be reduced to acceptable low levels. In this letter we will demonstrate experimentally the statistical distribution of the PDG given by [2]. This In this work the polarization dependent gain (PDG) fluctuations due to PMD in Raman amplified optical transmissions is experimentally demonstrated.

No presente trabalho é feito um estudo sistemático do efeito do campo cristalino nas propriedades ópticas do íon Er3+. Para tal propósito utilizamos três diferentes sistemas cristalinos dopados com Er3+: Ortovanadato de cálcio [Ca3(VO4)2], Niobato de lítio [LiNb03] e Titanato de bismuto [Bi12TiO20]. Os cristais foram crescidos no formato de fibras, pela técnica LHPG (Laser Heated Pedestal Growth). O uso deste método de crescimento permitiu não apenas o estudo do efeito do campo cristalino da matriz no Er3+ como também, a influência de diferentes condições crescimento. As composições dos cristais foram determinadas através de EDX (Energy Dispersive X Ray), XPS (X Ray Photoelectron Spectroscopy) e microscopia Auger. As amostras também foram investigadas através de absorção óptica e emissão, incluindo a determinação de seus índices de refração, gap óptico, identificação e análise de várias transições, medidas de emissão dependentes do tempo e da temperatura. A estrutura de todos os cristais foram investigadas pelas técnicas de difração de raios X e espalhamento Raman. Baseados nos resultados experimentais foi possível inferir sobre as regras impostas pelas condições de crescimento nas propriedades finais das fibras cristalinas de Ca3(VO4)2, LilNbO3 e Bi12Ti020 dopados com Er3+. Especificamente relacionado com as fibras cristalinas de Ca3(VO4)2 e LiNBbO3 dopadas com Er3+, a inserção de diferentes pressões de oxigênio molecular, durante o crescimento, induz mudanças significativas na sua estrutura cristalina. A inserção de íons Er3+ na matiz Bi12Ti020 produz uma luminescência fraca, quando comparada a do Ca3(VO4)2 e LiNbO3, porém esta luminescência apresenta um aumento considerável quando as amostras são co-dopada com íons Ga3+ / In this work we performed a systematic study of the crystal field effect on the optical properties of the Er3+ ion. For such a purpose we used three different crystalline Er3+ doped systems: calcium orthovanadate [Ca3(VO4)2, lithium niobate [LiNbO3] and bismuth titanate [Bi12TiO20]. The crystals were grown in the shape of fibers by the Laser Heated Pedestal Growth (LHPG) technique. By using this growth technique it was possible to explore not only the effects of different crystal fields on the Er3+ ion but also, the influence of different growth conditions. The composition of each fiber was determined from EDX (Energy, Dispersive X Ray , analysis), XPS (X Ray Photoelectron Spectroscopy) and Auger microprobe. The fibers were also optically investigated through optical absorption and emission and included the determination of their index of refraction, optical band gap, the identification and analysis of several different transitions, temperature and time-dependent measurements, etc. The structure of all crystals were investigated by X ray diffraction and Raman scattering techniques. Based on these experimental results it was possible to infer the role played by the growth technique and conditions on the final properties of these Er3+ -doped Ca3(VO4)2, LiNbO3 and Bi12Ti020 crystalline fibers. Specifically related to the Er3+ -doped Ca3(VO4)2 and LiNbO3 fibers, different pressures of molecular oxygen, during the groNvt.h., induces significant changes on their atomic (and electronic) structure. The insertion of Er3+ ions in the Bi12Ti020 matrix produces a small photoluminescence intensity, when compared with Ca3(VO4)2 and LINbO3, which is considerably increased by co-doping with Ga3+ ions

Neste trabalho apresentamos um cálculo teórico para o espalhamento Raman eletrônico via flutuações de densidade de spin de uma super-rede &#948-dopada de GaAs. A estrutura eletrônica da super-rede é determinada utilizando-se a teoria do funcional densidade dentro da aproximação de densidade local. O cálculo da seção de choque revela que sob condições de extrema ressonância existe uma forte dependência das formas de linha com a freqüência de excitação indicando a coexistência de um gás bi e tri-dimensional de elétrons nesta estrutura. Os resultados obtidos mostram excelente acordo entre teoria e experimento. / In this work we theoretically investigate the electronic Raman scattering by spin density fluctuations in periodically &#948-doped GaAs. The electronic structure of the superlattice is determined using density functional theory within the local-density-functional approximation. The calculation of the cross section reveals a strong dependence of the line shape on the exciting frequency under conditions of extreme resonance, which indicates the coexistence of a two and three-dimensional electron gas. The results show an excellent agreement between theory and experiment.

O presente trabalho aborda o estudo de correlações entre estrutura e propriedade de uma nova composição de vidros fluorofosfato. O trabalho compreende na síntese e caracterização de vidros fluorofosfatos com a seguinte composição: [80Ba(PO3)2 - 20Al(PO3)3]1-x[80BaF2 - 20AlF3]x(0 ≤ x ≤ 40 - mol%).Ressonância Magnética Nuclear e Espalhamento Raman são técnicas indicadas no estudo estrutural de materiais amorfos, como por exemplo, os vidros. Através dos resultados obtidos por difração de raios-X (DRX) e análise térmica diferencial (DTA) confirmam a formação de um sólido amorfo com concentrações de íons fluoretos de até 30 mol%. No entanto, a partir dos resultados da quantificação dos íons fluoretos via 19F RMN sugerem que houve uma quantidade significativa de perda de fluoreto ou ainda troca dos íons fluoretos por óxidos. Os espectros de 31P e Raman indicam uma gradual conversão das unidades Q2m em Q1m com o aumento de x. 19F RMN indica que os átomos de flúor estão em dois ambientes químicos distintos, onde os íons fluoretos estão ligados com átomos de fósforo ou distribuídos em um ambiente misto de Al/Ba. Resultados obtidos via 19F{31P}-REDOR confirmam a formação da ligação P-F. Os espectros de 27Al mostram a predominância dos átomos de alumínio com geometria octaédrica e ainda os resultados de 27Al{31P}-REDOR sugerem uma coordenação preferencial dos Al com unidades fosfato. Através dos resultados dos acoplamentos dipolares homonucleares via 31P{31P}-DRENAR corroboram com a deconvolução dos espectros de 31P na atribuição das espécies Q1m e Q2m. / In this work was studied the development of structure/property correlations for new fluorophosphate glasses compositions: [80Ba(PO3)2 - 20Al(PO3)3]1-x[80BaF2 - 20AlF3]x(0 ≤ x ≤ 40 - mol%). Most suitable techniques for the structural analysis in case of disordered and amorphous material are Nuclear Magnetic Resonance (NMR) Spectroscopy and Raman scattering. Results from X-ray diffraction (XRD) and differential thermal analysis (DTA) reveal that amorphous samples were obtained for all glass compositions up to x ≤ 30. However, the fluorine quantification via 19F MAS NMR suggests significant fluoride loss and/or fluoride/oxide replacement. Both 31P and Raman results indicate gradual conversion of Q2m units to Q1m units with increasing the fluorine concentration. 19F MAS NMR spectra indicate fluorine atoms in two different chemical environments bonded wither covalently to P-atoms or located in a mixed Al/Ba environment. The P-F assignment is confirmed by 19F{31P}-REDOR experiments. 27Al NMR spectra shows dominantly six-coordinated aluminium, and the 27Al{31P}-REDOR data suggest nearly exclusive coordination of Al with phosphate species. The dipolar coupling constant obtained by 31P{31P}-DRENAR are roughly consistent with 31P spectral deconvolution suggesting the presence of Q1and Q2 species.

The Warburg effect describes the survival advantage of cancer cells in that they can proliferate under low oxygen/hypoxic conditions via a less efficient pathway known as glycolysis. It has not yet been documented at which point, in an oxygen gradient, phenotypic changes occur. Measuring the intracellular redox potential (IRP) and its impact on cellular dynamics would provide greater insight into how disruption of redox homeostasis caused by changes in oxygen concentration leads to aberrant cell signalling and diseases such as cancer. Current techniques in measuring IRP include redox-sensitive fluorescent proteins such as roGFP which is glutathione-specific. Measuring the concentration of one redox couple is, however, not an accurate representation of IRP as it does not necessarily inform about the state of other redox couples. Furthermore, fluorescent biosensors can suffer from photobleaching and may interact with other oxidants. The IRP was measured, in this work, using our newly developed novel-class of surface enhanced Raman scattering nanoparticles which can quantitatively measure the redox potential of cells in vitro. A 'homemade' device was created to keep the cells under fixed pO2 whilst obtaining measurements. The IRP was correlated with the transcriptomic and downstream metabolic profiles of MCF7 breast cancer cells, under perturbed pO2, using 1H NMR spectroscopy (NMR), mass spectrometry (MS) and RNA-sequencing. Discriminatory metabolites were all associated with energy and glucose metabolism. Discriminatory microRNAs were all affiliated with the hallmarks of cancer; the regulation of some is controlled by transcription factors containing redox-sensitive motifs in their DNA binding domains. Multivariate analysis techniques were used to analyse the different data streams in a holistic way that allows the correlation of redox potential, metabolism and transcription.

Protein engineering strategies, such as directed evolution, generate large libraries of enzyme variants, typically in the range of 106-108 variants. However, the availability of rapid, robust high-throughput screening methods has often limited the impact of directed evolution in discovering enzymes with enhanced catalyst performance. Raman spectroscopy is an established analytical technique, providing molecular specific information, permitting analysis in aqueous solutions and as such is an attractive, alternative screening method for biological systems. Although an inherently weak physical phenomenon, enhanced Raman scattering techniques, such as surface enhanced Raman scattering (SERS) and ultraviolet resonance Raman (UVRR) spectroscopy, can be used to overcome the associated sensitivity issues. Herein, we successfully monitored xanthine oxidase (XO) catalysed conversions of xanthine to uric acid, before extending to hypoxanthine, using two contrasting Raman scattering enhanced approaches. Firstly, a SERS-based assay was developed utilising silver nanoparticles to measure analytes directly and quantitatively on micromolar scale, in the absence of chromogenic substrates or lengthy chromatography. Secondly, a UVRR approach was developed enabling monitoring of the XO-mediated reaction in real-time and without the need to quench the system. Significantly, both methods demonstrated over &gt;30 fold reduction in acquisition times (when compared to conventional HPLC analysis), and offered excellent medium-term reproducibility and accuracy of results over significant time periods. Furthermore, investigations were made into developing this SERS-based assay into an enantiomeric screen using another vibrational spectroscopy approach, Raman optical activity (ROA), along with circular dichroism (CD). Successful chiral reduced nanoparticles were synthesised, with multiple characterisation techniques employed, affording enantiopure Au-cysteine and Ag-tyrosine colloids. However, it was not possible to generate consistent and reproducible SEROA responses, with these techniques ultimately being unsuccessful in analysing these chiral sensitive nanoprobes, and thus differentiating between the D- and L- forms. Finally, a novel SERS-based approach, in combination with the standard addition method (SAM), was developed for the routine analysis of uric acid (end product in XO catalysed reaction(s) and biomarker for various diseases), at clinically relevant levels in urine samples from patients. Results were highly comparable and in very good agreement with HPLC analyses, with an average < 9% difference in predictions between the two analytical approaches across all samples analysed, and a 60-fold reduction in acquisition time (when compared with HPLC). Together, the research presented in this thesis demonstrates the suitability of Raman enhanced techniques for quantitative analysis, measuring the analytes directly using a portable Raman instrument and, most importantly, offering significant reductions in acquisition times when compared to established analytical techniques.

This thesis presents results of studies using the technique of surface-enhanced Raman scattering (SERS) spectroscopy to investigate surface processes occurring on gold during electrochemical experiments in thiosulfate solutions and during leaching in ammoniacal copper(II) thiosulfate systems. The gold SERS electrode was characterised using X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), X-ray diffraction (XRD), energy dispersive X-ray analysis (EDX), linear sweep voltammetry (LSV) and cyclic voltammetry (CV). SEM investigations of the SERS activated gold surface showed the presence of electrodeposited dendrites with nanoscale features. XRD studies of the dendrites showed them to be polycrystalline with a large proportion of Au(111). Rotating disk electrode (RDE) studies of polished and SERS electrodes were undertaken in order to clarify the electrochemistry of various thiosulfate systems. The ex situ techniques of XPS and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy were used to determine the presence of sulfur, copper and nitrogen on leached or electro-oxidised surfaces. Voltammetric methods were used to determine sulfur and copper surface coverages at various potentials in sulfide, thiosulfate and ammoniacal copper(II) thiosulfate media. The electro-oxidation of sulfide was examined as a model system in order to identify spectral features and coverage associated with various potential-dependent sulfur layers. In the hydrogen evolution region, a surface layer formed by underpotential deposition in acid and basic media was characterised by a gold-sulfur stretching band, Au-S, attributed in the literature to a monoatomic stretching mode of sulfur bonded to gold. The surface coverage in this potential region was limited to 0.35 ML, representing adsorption in a (3x3)R30 structure. Bands were found to be absent that would have indicated the adsorption of SH– species as has been reported in the literature. A facile change in the position of the Au-S band with potential, unaccompanied by Faradaic processes, was seen when the adsorbed (3x3)R30 sulfur layer was examined in a sulfide-free solution. This may indicate a change in sulfur adsorption sites with potential in the hydrogen evolution region. At potentials above the S II/S0 reversible value in sulfide solutions, the surface coverage increased and S-S bands were observed, indicating the formation of an adsorbed polysulfide species, Au-Sn. A change in the position of the Au-S band was seen to accompany the formation of the S-S bands. As coverage further increased, bands due to S-S-S bending, S-S-S, developed that were characteristic of cyclo octasulfur, S8. On removal from sulfide solution and rinsing, a characteristic SERS spectrum was observed ex situ. The spectrum showed a characteristic S-S at 460 cm-1 and Au-S at 325 cm-1 and was assigned to an adlayer of S8 adsorbed on gold in a crown configuration, Au S8. Gold was polarised in thiosulfate solutions at a potential at which gold dissolution is known to occur. In situ SERS spectra showed bands characteristic of S-S bonding and Au2S to occur after 1 hr for thiosulfate with sodium and ammonium counter-ions and for both systems in the presence of ammonia. XPS studies of polished gold held in sodium thiosulfate under these conditions showed S 2p binding energies corresponding to metal sulfide and pyritic sulfur, S22-. After 72 hrs at the mixed potential in air saturated sodium thiosulfate, SERS investigations showed a spectrum with Au-S8 characteristics. XPS studies on a polished electrode under these conditions showed a third type of S 2p binding with a binding energy between that of pyritic sulfur and S8. The sodium thiosulfate system showed an adsorbed tetrathionate-like surface species, Au-S4O6, to be present at the mixed potential and to disappear with increased potential prior to the formation of bulk S8 via an Au-S8 intermediate. In the presence of the ammonium cation at high potentials, Au-Sn bands appear in the presence of a more intense and broad Au-S characteristic of gold sulfide, Au2S. This was assigned to a mixed gold sulfide/polysulfide phase, Au2S/Sn. With addition of ammonia, the surface species Au S4O6, Au2S/Sn and, tentatively, adsorbed NH3 were observed above the mixed potential. For gold in air-saturated copper(II) ammoniacal thiosulfate media, bands due S-S at 382 cm-1 and symmetric S-O stretching, symS-O, at 1017 cm-1 developed during leaching at the mixed potential. These modes diminished and, when rinsed and examined in water, were replaced by a single band at 255 cm 1 assigned to a metal sulfide stretch. In typical leach solutions, sulfur and copper coverages showed a 2:1 atomic ratio after leaching for 16 h. Ex situ ATR and XPS studies showed that ammonia was adsorbed to a surface copper sulfide. Kinetic studies using atomic absorption spectroscopy (AAS) to measure gold in solution showed that the ammoniacal copper(II) thiosulfate leaching solution exhibited higher dissolution rates in the presence of the sodium counter ion than the ammonium. Thiourea as an additive to thiosulfate solutions was seen to disrupt S-S bonding in both Au-S8 and Au2S/Sn surface structures.

The main theme of this thesis is to study effects of different environments on geometric and electronic structures, as well as optical responses, of molecules using time-(in)dependent density functional theory. Theoretical calculations have been carried out for properties that can be measured by conventional and advanced experimental techniques, including one-photon absorption (OPA), two-photon absorption (TPA), surface-enhanced Raman scattering (SERS) and second order nonlinear optical (NLO) response. The obtained good agreement between the theory and the experiment allows to further extract useful information about inter- and intra-molecular interactions that are not accessible experimentally. By comparing calculated one-photon absorption spectra of aluminum phthalocyanine chloride (AlPcCl) and AlPcCl -water complexes with the corresponding experiments, detailed information about the interaction between water molecules and AlPcCl, and geometric changes of AlPcCl molecule has been obtained. Effects of aggregation on two-photon absorption spectra of octupolar molecules have been examined. It is shown that the formation of clusters through inter-molecular hydrogen bonding can drastically change profiles of TPA spectra. It has also demonstrated that a well designed molecular aggregate/cluster, dendrimer, can enhance the second order nonlinear optical response of the molecules. In collaboration with experimentalists, a series of end-capped triply branched dendritic chromophores have been characterized, which can lead to large enhancement of the second order NLO property when the dipoles of the three branches in the dendrimers are highly parallelized. Surface-enhanced Raman scattering has made the detection of single molecules on metal surface become possible. Chemically bonded molecule-metal systems have been extensively studied. We have shown in a joint experimental and theoretical work that stable Raman spectra of a non-bonding molecule, perylene, physically adsorbed on Ag nano-particles can also be observed at low temperature. It is found that the local enhanced field has a tendency to drive molecule toward a gap of two closely lying nano-particles. The trapped molecule can thus provide a stable Raman spectrum with high resolution when its thermal motion is reduced at low temperature. For the ever growing size of molecular complexes, there is always the need to develop new computational methods. A conceptually simple but computationally efficient method, named as central insertion scheme (CIS), is proposed that allows to calculate electronic structure of quasi-periodic system containing more than 100,000 electrons at density functional theory levels. It enables to monitor the evolution of electronic structure with respect to the size of the system. / QC 20100823

Lung carcinoma is the most prevalent type of cancer in the world, considered to be a relentlessly progressive disease, with dismal mortality rates to patients. Recent advances in targeted therapy hold the premise for the delivery of better, more effective treatments to lung cancer patients, that could significantly enhance their survival rates. Optimizing care delivery through targeted therapies requires the ability to effectively identify and diagnose lung cancer along with identifying the lung cancer cell type specific to each patient, \textit{small cell carcinoma}, \textit{adenocarcinoma}, or \textit{squamous cell carcinoma}. Label free optical imaging techniques such as the \textit{Coherent anti-stokes Raman Scattering microscopy} have the potential to provide physicians with minimally invasive access to lung tumor sites, and thus allow for better cancer diagnosis and sub-typing. To maximize the benefits of such novel imaging techniques in enhancing cancer treatment, the development of new data analysis methods that can rapidly and accurately analyze the new types of data provided through them is essential. Recent studies have gone a long way to achieving those goals but still face some significant bottlenecks hindering the ability to fully exploit the diagnostic potential of CARS images, namely, the streamlining of the diagnosis process was hindered by the lack of ability to automatically detect cancer cells, and the inability to reliably classify them into their respective cell types. More specifically, data analysis methods have thus far been incapable of correctly identifying and differentiating the different non-small cel lung carcinoma cell types, a stringent requirement for optimal therapy delivery. In this study we have addressed the two bottlenecks named above, through designing an image processing framework that is capable of, automatically and accuratly, detecting cancer cells in two and three dimensional CARS images. Moreover, we built upon this capability with a new approach at analyzing the segmented data, that provided significant information about the cancerous tissue and ultimately allowed for the automatic differential classification of non-small cell lung carcinoma cell types, with superb accuracies.