Le présent travail de thèse a consisté en un diagnostic d’une colonne de plasma d’un mélange d’argon et de CO2, créée par une décharge éclatant dans un réacteur cylindrique, entre deux électrodes pointues en tungstène, sous une tension d’amorçage de 10KV, un courant de 100 à 300mA, et à pression atmosphérique. Le diagnostic du plasma a été réalisé à l’aide d’un laser Hélium Néon (raie 632.8nm), d'un interféromètre de Mach-Zehnder et d’un spectromètre à fibre optique. Après calcul de la composition du mélange d’Argon et de CO2 en fonction de la température par la méthode de minimisation de l’enthalpie libre de Gibbs, on a déterminé la densité des espèces. Utilisant les propriétés des particules soumises à une onde électromagnétique, et la relation de Gladstone Dale qui lie l’indice de Réfraction d’un Gaz à sa densité et à sa température, nous avons calculé l’évolution de la réfractivité du milieu. Ensuite nous l’avons mesurée pour obtenir les profils radiaux de température par la transformée de Fourier et l’inversion d’Abel, des cartes de phase obtenues par interférométrie optique. Ce travail a été complété par une analyse par spectroscopie optique moléculaire d’émission. Utilisant le système de Swan de la molécule C2 (d3!g – a3!u) comme pyromètre, notamment les bandes 01(5635.2 Å) et 12 (5585.5 Å), nous avons déterminé les températures vibrationnelles et rotationnelles du plasma. Un programme en FORTRAN a été mis au point, pour la simulation des bandes moléculaires. Nous avons diagnostiqué la colonne de plasma sur toute sa largeur et dressé un profil de température radial. Les températures vibrationnelles et rotationnelles nous ont permis de calculer l’écart à l’équilibre thermodynamique. / This work of thesis consisted of a diagnosis of a column of plasma of a mixture of argon and CO2 created by a discharge bursting in a cylindrical engine, between two pointed tungsten electrodes, under a voltage of 10KV, a current of 100 to 300mA, at atmospheric pressure. The diagnosis of plasma was carried out using a laser Helium Neon (line 632.8nm), of an interferometer of Mach-Zehnder and a spectrometer with optical fibre. After calculation of the mix design of Argon and CO2 according to the temperature by the method of minimization of the free enthalpy of Gibbs, one determined the density of the species. Using the properties of the particles subjected to an electromagnetic wave, and the relation of Gladstone Dale which binds the index of Refraction of a Gas to its density and its temperature, we calculated the evolution of the refractivity of the medium. Then we measured it to obtain the radial profiles of temperature by the Fourier transform and the inversion of Abel, of the charts of phase obtained by optical interferometry. This work was supplemented by an analysis by molecular optical spectroscopy of emission. Using the system of Swan of the molecule C2 (d3!g – a3!u) like pyrometer, in particular the bands 01(5635.2 Å) and 12 (5585.5 Å), we determined the vibrational and rotational temperatures in the plasma. A Fortran program was developed, for the simulation of the molecular bands. We diagnosed the column of plasma over all its width and drew up a radial profile of temperature. The calculation of the vibrational and rotational temperatures enabled us to calculate the variation with thermodynamic balance.

L’analyse des gaz d’échappement des moteurs à combustion interne a été traditionnellement réalisée en laboratoires en utilisant des analyseurs de gaz en vrac avec des équipements coûteux. Afin de créer un système capable de réaliser le travail de ces analyseurs, un capteur pouvant détecter plusieurs gaz simultanément est indispensable pour en mesurer la concentration. En effet, utiliser un capteur pour chaque gaz est couteux et peut amener à des procédures complexes d’analyse en raison des différentes technologies utilisées. De plus, l’utilisation de multiples capteurs donne lieu à une perte de ressources financières et humaines. Pour pallier ce problème, une approche alternative proposée dans cette thèse consiste à utiliser un seul capteur pour l’analyse simultanée des différents gaz. Cette approche contribue à réduire la complexité des analyses, la taille et la collecte de données des mesures de gaz mentionnés précédemment. Elle permet également la baisse du coût de l’ensemble du système des mesures.Cette thèse présente la conception, la méthodologie et le développement d’une nouvelle approche pour la mesure de la concentration de gaz utilisant le traitement d’images numériques à travers la modélisation du mélange des couleurs d’émission de lumière dans le tube de décharge de gaz. L’application du modèle inverse permet d’obtenir le pourcentage de chaque gaz dans un mélange contenant jusqu'à quatre gaz connaissant la couleur d’émission du mélange et la couleur d’émission de chaque gaz. Nous discutons aussi le potentiel de certaines méthodes quant à leurs propriétés de miniaturisation et leurs limites. Une comparaison entre les différents capteurs miniaturisés est réalisée en termes suivant la sensibilité, la sélectivité, le coût et d’autres conditions. Pour atteindre les objectifs de recherche, les problèmes techniques rencontrés tels que la modélisation de mélange des couleurs, l’étalonnage de capteurs pour l’acquisition d’images, et le traitement des erreurs de mesures ont été identifiés et des solutions ont été proposées. / Gases represent one of the most important key measurands in many industrial and domestic activities. The need to detect single gas or a group of gases at the same time varies from one application to another. One of the most important applications of gas sensing is in the concentration measurement of exhaust emissions in internal combustion engines. The variety of gases emitted by these engines and the necessity for a precise measurement of their concentrations are the major incentives for researchers to develop gas sensors that are not only limited to a certain type of gases but to a variety of gases. The most interest gases include CO, NO, NO2, NH4, SO2, CO2, CH4 and other hydrocarbons. These gases can be harmful to human health if present beyond a certain concentration. The analysis of exhaust emissions of internal combustion engines has traditionally been achieved in laboratories using bulk gas analyzers and costly equipments. In order to create a system which can do the work of these analyzers, a sensor that can measure the concentration of multiple gases at the same time is needed. Instead of using a sensor for each gas which is costly and introduce another complexity to the analysis procedure due to the different technologies that are used in the detection of different types of gases. This directly translates into loss of financial and human resources that could otherwise be productively used. In an effort to remedy this situation, this dissertation proposes an alternate approach that uses one sensor to analyze multiple gases simultaneously. This has a significant potential in reducing the aforementioned complexity, size and data collection tasks, and at the same time can lower the cost of the overall system.This dissertation presents the design, methodology, and development of a new method for gas concentration measurement using digital image processing through modeling the color mixing of light emissions in gas discharge tube. The application of the inverse model allows us to get the percentages of each gas in a mixture of up to four gases knowing already the color of emission of the whole mixture and the color of emission of each gas alone. It also discusses the miniaturization potential of some of the methods that are promising in the ability of their miniaturization but suffer from different problems. A comparison is also done among the miniaturized sensors in terms of different parameters like sensitivity, selectivity, cost and other terms. In achieving the research objectives, major technical challenges such as color mixing modeling, imaging sensor calibration, and measurements’ error handling have been successfully identified and addressed.

The application of low-pressure low-temperature hydrogen plasma on artificial corrosion layers on bronze has been studied. For this purpose, three sets of bronze corroded samples were prepared. The first step of the model sample preparation was grinding of the bronze surface by using emery with 60, then 280 and finally by 600 grains density, in order to achieve the defined surface roughness. The next step of the work were optical and scanning electron microscopy observations with energy dispersive X-ray micro analysis (SEM-EDX) of the prepared bronze sample for purpose of surface structure characterization and element composition determination. Bronze samples with defined surface structure were corroded in different corrosion atmospheres. Three different model corrosion layers were formed by acidic atmospheres of hydrochloric acid, nitric acid and sulphuric acid. The element composition and structure of corrosion layer was determined by SEM-EDX again. The different amounts of oxygen, nitrogen, chlorine, sulfur, copper, tin and lead in the corrosion layer according to different types of corrosion atmospheres were determined. The next and also main part of the work was a plasma chemical reduction of corroded samples. The plasma reactor used the RF discharge (13.56 MHz) created in quartz tube with outer electrodes. The generation of capacitively coupled plasma in continuous or pulse mode by different supplied power was carried out. The plasma radiation emitted from the RF discharge during the sample treatment was measured by optical emission spectroscopy. The quantity of OH radical created in an active discharge by reactions of atomic hydrogen with the corrosion layer is a significant indicator of a reduction process. Therefore the OH radical band integral intensities observed as a function of the treatment time were used as a monitor for plasma chemical reduction process. The OH emission showed different behavior depending on corrosion layer composition during the plasma treatment. The transformations of the corrosion layer due to the plasma effect were investigated by means of SEM-EDX once again. Changes in the element composition of corrosion (or surface) layers in consequence of plasma chemical treatment are given. Generally, the element composition after the plasma chemical treatment showed explicitly that oxygen and chlorine content in the corrosion layer decreased, nitrogen was removed totally. Metal deposition on the reactor wall was observed occasionally. The SEM-EDX analyzes also showed that in some cases the tin content in sample surface layers was significantly decreased. For that reason, in case of bronze sample (artifacts) treatment, the sample and plasma temperature seem to be very important parameters for the process optimization. The acceptable conditions for plasma chemical treatment has been found in case of corrosion layer formed by nitric acid, only. The other corrosions will be a subject of further studies.

The aim of this thesis is diagnose post-discharge nitrogen plasma with optical emission spectroscopy. There is long interest of investigated of nitrogen post-discharge plasma and study how to use it in theory as well as in practice. All results were measured with method of optical emission spectroscopy of post-discharge plasma. Discharge was generated by direct-current voltage generator with flowing regime. In this thesis was used for different series of experiments. First experiment was performed with adding water vapour into argon plasma. Measuring was processed at constant current 140 mA, voltage 1.5 V and pressure 1 000 Pa. It was changed flow rate and for each individual flow rate was measured in range 1–25 cm from end of active discharge. Second experiment was with adding nitrogen into argon plasma. Measuring was processed at constant current 140 mA, voltage 1.5 V and pressure 1 000 Pa. We were changing flow rate of nitrogen (0,2 sccm, 0,4 sccm and 0,8 sccm). For each individual flow rate was same experiment with changing distance from active discharge. Third experiment was about adding mercury vapour into nitrogen post-discharge. Measuring was processed at constant current 120 mA, voltage 3.5 V and pressure 1 000 Pa. Measuring was performed with two configuration: with diaphragm and without it. Last experiment was about adding air into argon plasma. Measuring was processed at constant current 140 mA, voltage 1.0 V and pressure 1 000 Pa. Temperature of outer face of tube was measured by thermocouple and infrared thermometer, was measured for last two experiments (argon – air and nitrogen). During experiments with pure nitrogen was visible phenomenon called pink afterglow which is manifested by noticeable increase pink coloration. Optical emission spectrums post-discharge was take at various range of wavelength. At argon with water vapour was 280–600 nm and at adding nitrogen into argon was at range 320–500 nm. At added mercury vapour into nitrogen was 320–600 nm. For experiment argon – air was wavelength range 320–600 nm. From results of experiments were designed dependencies of calculated intensity from measured spectra on distance from active discharge. Also were constructed dependencies of measured temperature on distance from active discharge.

In the present work, the abnormal glow discharge at atmospheric pressure was generated in the nitrogen-methane (1 to 5 %) gaseous mixtures related to the atmosphere of Titan. The discharge itself was monitored by optical emission spectrometry that confirmed presence of active nitrogen species and various radicals formed from methane. Besides them, the CN spectral bands were observed. Intensities of all light emitting species were studied in the dependence on applied power and composition of nitrogen-methane mixture. The rotational temperature of about 2000 K was calculated from the second positive nitrogen system. The vibrational temperature also obtained from neutral nitrogen molecule increased nearly directly with methane from 3000 K (1 % CH4) to 3600 K (5 % CH4). In the contrary, vibrational temperature obtained from nitrogen molecular ion decreased with methane in the gaseous mixture and increased with applied discharge power from 3700 K to 4200 K. The same trend showed the vibrational temperature calculated from violet system of CN with value from 4600 K to 5800 K. The stable discharge products were analysed by proton transfer time of flight mass spectrometry of the exhausting gas. Presence of many aliphatic and some aromatic hydrocarbons was confirmed as well as quite a lot of amino and cyano compounds. Increasing concentrations of methane have produced more substances with higher molecular weight and less simple substances that were likely to be consumed on more complex substances. Their relative intensities were determined under the same conditions as optical emission spectra were collected.

Abstract In this thesis, different spectroscopic methods are used for studying metals. Electron spectroscopy is applied for the study of binding energy shifts between atomic vapor and solid metals. Photoionization and Auger decay of high temperature aluminum vapors are investigated. Ionization of atomic chromium metal vapor by light absorption is studied with synchrotron radiation and time-of-flight ion mass spectroscopy. Optical spectroscopy is used for studying light emission from electric arc furnace plasma in experimental apparatuses developed during this work. Experimental techniques and sample preparation methods are presented. / Original papers The original publications are not included in the electronic version of the dissertation. Huttula, M., Jänkälä, K., Mäkinen, A., Aksela, H., & Aksela, S. (2008). Core shell electron spectroscopy on high temperature vapors: 2s photoionization and Auger decay of atomic aluminium. New Journal of Physics, 10(1), 13009. https://doi.org/10.1088/1367-2630/10/1/013009 Huttula, M., Partanen, L., Mäkinen, A., Kantia, T., Aksela, H., & Aksela, S. (2009). KLL Auger decay in free aluminum atoms. Physical Review A, 79(2). https://doi.org/10.1103/physreva.79.023412 Aksela, S., Kantia, T., Patanen, M., Mäkinen, A., Urpelainen, S., & Aksela, H. (2012). Accurate free atom–solid binding energy shifts for Au and Ag. Journal of Electron Spectroscopy and Related Phenomena, 185(8–9), 273–277. https://doi.org/10.1016/j.elspec.2012.05.007 Mäkinen, A., Patanen, M., Aksela, S., & Aksela, H. (2012). Atom-solid 3p level binding energy shift of transition metals Cr, Mn, Fe, Co, and Ni. Journal of Electron Spectroscopy and Related Phenomena, 185(12), 573–577. https://doi.org/10.1016/j.elspec.2012.12.006 Mäkinen, A., Niskanen, J., & Aksela, H. (2012). Relative photoionization cross section of Cr atoms in the valence region. Physical Review A, 85(5). https://doi.org/10.1103/physreva.85.053411 Mäkinen, A., Niskanen, J., Tikkala, H., & Aksela, H. (2013). Optical emission from a small scale model electric arc furnace in 250–600 nm region. Review of Scientific Instruments, 84(4), 43111. https://doi.org/10.1063/1.4802833

The aim of this master thesis is to study the influence of metallic atoms on nitrogen post-discharge. Pure nitrogen post-discharge is a subject study of many works dealing with kinetic processes in plasma. Unfortunately, there are only a few published works that present influence of various traces on nitrogen post-discharge kinetics. This master thesis deals with problems of nitrogen post-discharge containing mercury traces. All experimental data were obtained using optical emission spectroscopy of a DC discharge in a flowing mode, which can achieve appropriate temporal resolution in the order of milliseconds. Spectra emitted during the post-discharge were recorded in the range of 320-780 nm and the following molecular spectral systems were identified: • 1. positive system of nitrogen: N2(B) -> N2(A), • 2. positive system of nitrogen: N2(C) -> N2(B), • 1. negative system of nitrogen: N2+(C) -> N2+(X), • NO-beta system: NO(B) -> NO(X). Besides them we were able to record the mercury line at 254 nm, only (in the spectrum of the first as well as in the second order); no other mercury lines were observed. The mercury vapor was introduced into the system at selected post-discharge time. Dependence of selected molecular band head intensities as well as mercury line intensity on experimental conditions (pressure, discharge power, wall temperature, time of mercury vapor introduction) were observed in time evaluation. The data obtained in pure nitrogen were used as a reference. The obtained results showed very high sensitivity of kinetic processes on mercury atoms presence. If mercury was introduced into the post-discharge the mercury line was observable around the site where mercury vapor was introduced into the discharge. The experimental data showed that mercury line intensity was directly proportional to the mercury atoms concentration and saturation effect could be observed. The energy level diagram demonstrates that the observed mercury line can be excited by collisions with nitrogen ground state molecule excited to vibrational level 18. Thus the mercury can be used for the monitoring of population at this vibrational level. Finally we obtained the population profile at this nitrogen metastable level during the post-discharge. The presented work demonstrates possibility of mercury atoms application for the monitoring of one nitrogen metastable state. Unfortunately, the contemporary data are not sufficient for the measurement of metastable absolute concentration. However, complex understanding of nitrogen post-discharge kinetics is still an open problem. Therefore a lot of future work should be done although the presented work brings a good fundament for such research.

Nonthermal plasma-assisted combustion (PAC) has been demonstrated to be a promising potential method to enhance combustion performance and reduce the pollutant emissions. To better understand the mechanism in PAC, we have conducted a series of studies on the combustion enhancement by plasma using a home-developed PAC platform which employs a nonthermal microwave argon plasma and a suit of optical diagnostic tools including optical imaging, optical emission spectroscopy, and cavity ringdown spectroscopy. A new PAC system in which a continuous atmospheric argon microwave plasma jet is employed to enhance combustion of methane/air mixtures was reported. Reactive species in PAC were characterized in a state-resolved manner including the simultaneously measurements of OH(A) and OH(X) radicals in the PAC flames. Roles of the state-resolved OH(A) and OH(X) radicals in microwave PAC of premixed methane/air mixture were explored. It was concluded that if both OH(A) and OH(X) radicals assisted the ignition and flame stabilization processes, then we may hypothesize that the role of OH(A) was more dominant in the ignition enhancement but the role of OH(X) was more dominant in the flame stabilization. The effect of fuel injection configurations was investigated in the comparative study between PAC of the premixed and nonpremixed methane/air mixtures. It was found that emissions from the CH (A-X) and C2 Swan systems only exist in the nonpremixed PAC which suggest that the reaction pathways are different between premixed and nonpremixed PAC. The PAC of premixed methane/oxygen/argon mixtures was investigated. A U-shaped dual-layer curve of fuel ignition/flame stabilization limit showing the effects of the plasma power on the fuel ignition and flame stabilization was observed and reported. A parametric study of the microwave PAC of the premixed ethylene/air mixtures was conducted. Behavior of the OH, CH, and C2 radicals and their dependence on plasma power, argon flow rate, and total ethylene/air mixture flow rate were also studied.

The method of optical emission spectroscopy has been used with Fe-Ni and other complex alloys to investigate in-situ compositional control for additive manufacturing. Although additive manufacturing of metallic alloys is an emerging technology, compositional control will be a challenge that needs to be addressed for a multitude of industries going forward for next-gen applications. This current scope of work includes analysis of ionized species generated from laser and metal powder interaction that is inherent to the laser engineered net shaping (LENS) process of additive manufacturing. By quantifying the amount of a given element's presence in the electromagnetic (EM) spectrum, this amount can be compared to the actual amount present in the sample via post-processing and elemental dispersive x-ray (EDX) data analysis. For this work a commercially available linear silicon CCD camera captured metallic ion peaks found within the ultraviolet (UV) region to avoid background contamination from blackbody radiation. Although the additive manufacturing environment can prove difficult to measure in-situ due to time dependent phenomena, extreme temperatures, and defect generation, OEM was able to capture multiple data points over a time series that showed a positive correlation between an element's peak intensity and the amount of that element found in the final deposit.

<p>In this work a flow stabilized corona torch plasma was used for periodic domain inversion of MgO-doped lithium niobate with 19 .1 μm periodic gratings. The effective non-linear coefficient (derr) achieved through corona discharge poling was 17.5 pm/V, which agrees well with theoretical value of 16~19 pm/V. By analysing the second harmonic generation (SHG) tuning curves, the grating uniformity over the 10 mm grating was investigated. The 0.6 run bandwidth of the SHG tuning at full width half maximum (FWHM) corresponded exactly to the theoretical value. The agreement between experimental data and theoretical results imply that the obtained periodically poled lithium niobate (PPLN) has high quality. By controlling temperature in the range of 20 °C to 120 °C tunability of SHG wavelength was demonstrated between 782 run and 788 run.</p> <p>Discharge characteristics of the corona were studied using a floating potential double probe and optical emission spectroscopy. Using the double probe the distribution of ion density downstream of the corona torch was observed. The maximum ion density of 2 x 1018 (ions/cm3) was achieved 2 mm below the discharge electrode. Measurement of the optical emission spectrum was used to determine the vibrational ion temperature to be 3953 K. The observed spectrum consisted entirely of the second positive band of nitrogen.</p> <p>The applied voltage range of 9 kV to 10 kV was observed to be optimum for domain growth in periodic poling. Poling uniformity of the 12 mm grating was optimized for an electrode to crystal spacing of 13 mm. Increasing the crystal temperature during poling reduces the required coercive field for domain inversion. This reduces the required applied voltage and also reduces the required poling time by increasing the domain-switching rate. Proton exchange pretreatment of the (+z) crystal surface prior to poling has been demonstrated to control domain spreading, however future efforts are required to ensure a more reliable nucleation condition. Both high vacuum and spin coated photoresist function to increase electrical discrimination of anode grating and provide an improved nucleation condition for periodic poling of MgO-doped lithium niobate. Poling uniformity of the 12 mm grating was optimised for an electrode to crystal spacing of 13mm.</p> / Thesis / Master of Applied Science (MASc)