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The nature of work conducted during the course of study towards a MSc degree focused on tunable diode laser absorption spectroscopy (TDLAS). This field involves the in-situ detection of gas constituents from low concentration samples. Specifically, I will focus on TDLAS systems utilizing practical optics, readymade electronics, and commercially available near infrared vertical cavity surface emitting lasers (VCSEL). In attempting to lower the minimum detectable concentrations of constituent gases, quantifying contributory noise sources is vital. Consequently, I seek to characterize principle noise sources of a prototypical TDLAS system in order to gain understanding of the limits that inhibit detection of trace gas concentrations. The noise sources which were focused on can be categorized as follows: source laser noise, optical noise, and detection noise. Through this work it was my goal to provide the means of achieving superior sensitivities.

La mesure des polluants fait l'objet depuis la fin du XXème siècle d'une attention toute particulière pour la préservation de la planète. Les espèces gazeuses, plus précisément le méthane, présent dans le MIR, possède des forces de raies très intenses, ce qui rend la technique plus sensible. La technique de détection de gaz utilisée durant ma thèse est choisie après une large comparaison entre différentes techniques appartenant à la SDLA. Cette technique est la technique QEPAS. Elle a montré depuis son invention en 2002, une grande sensibilité et sélectivité dans le domaine d'analyse de gaz. La source de lumière utilisée dans la QEPAS est une diode laser accordable (laser à SC), ce qui permet de rendre la technique plus sélective, en variant sa longueur d'onde d'émission en fonction du courant injecté et/ou température de régulation, pour se localiser sur une raie souhaitée à détecter. Le détecteur de la QEPAS est le diapason à quartz (QTF). Ce dernier est très sensible à la force minime appliquée par l'onde acoustique, ce qui rend la technique très sensible aux faibles concentrations. Plusieurs étapes de caractérisations sont exigées pour déterminer les caractéristiques de la diode laser et du QTF. Après le choix de la diode laser et du QTF, idéaux pour la spectroscopie, on passe à l'évaluation de la technique QEPAS dans le domaine d'analyse de gaz. Les limites de détection du méthane obtenues avec la technique QEPAS sont 0.8 ppmv et 400 ppbv à 2.3 µm avec un laser à Fabry-Pérot et un laser à cristaux photoniques, respectivement, et 100 ppbv à 3.3 µm avec un laser DFB.Ce travail a permis d'obtenir une technique performante (sensible, sélective, pas cher…), dans le domaine d'analyse de gaz. / The measurement of the pollutants is the subject since the late twentieth century especially in attention to protecting the planet. The gaseous species, specifically methane, present in the MIR, has strengths rays very intense, making the technique more sensitive.The detection technique of gas used during my PhD was chosen after an extensive comparison of different techniques belonging to the SDLA. This technique is the QEPAS technique. It has shown since its invention in 2002, a high sensitivity and selectivity in gas analysis. The light source used in the QEPAS is a tunable diode laser (Laser SC), thus making the technique more selectively, by varying the wavelength of emission as a function of injected current and / or control temperature to be located on a line desired to detect. The detector is QEPAS of quartz tuning fork (QTF). The latter is very sensitive to small force applied by the acoustic wave, which makes the technique very sensitive to low concentrations. Several steps are required characterization to determine the characteristics of the laser diode and the QTF. After choosing the laser diode and the QTF, ideal for spectroscopy, we pass to the evaluation of the technique QEPAS in gas analysis. The detection limits of methane obtained with the technique are QEPAS 0.8 ppmv and 400 ppbv to 2.3 microns with a Fabry-Perot laser and a photonic crystal laser, respectively, and 100 ppbv to 3.3 microns with a DFB laser.This work has provided a powerful technique (sensitive, selective, cheap ...) in gas analysis.

<p>This work presents the development and/or application of several laser diagnostics for studying the flame structure of composite propellant flames. These studies include examining the flame structure of novel energetic materials with potential as propellant ingredients, the near-surface flame structure of basic composite propellants, and the global flame structure of propellants containing metal additives.<br></p><p><br></p><p>First, the characterization of the deflagration of various novel energetic cocrystals is presented. The synthesis and development of novel energetic materials is a costly and challenging process. Rather than synthesizing new materials, cocrystallization provides the potential opportunity to achieve improved properties of existing energetic materials. This work presents the characterization of the effect of cocrystallization on the deflagration of a 2:1 molar cocrystal of CL-20 and HMX as well as a 1:1 molar cocrystal of CL-20 and TNT. A hydrogen peroxide (HP) solvate of CL-20 as well as a polycrystalline composite of HMX and ammonium perchlorate (AP) were also studied. A physical mixture of each material was also tested for comparison. The burning rate of each material was measured as a function of pressure. Flame structure during self-deflagration was examined using planar laser-induced fluorescence (PLIF) of CN and OH. The burning rate of the HMX/CL-20 cocrystal and the CL-20/HP solvate closely matched that of CL-20, but the burning rate of the TNT/CL-20 cocrystal was between the burning rate of its coformers. All HMX/AP materials had a higher burning rate than either HMX or AP individually and the burning rate of a physical mixture was found to be a function of particle size. The differences in the burning rate of the physical mixtures and composite crystal of HMX/AP can be explained by changes in the flame structure observed using PLIF. Burning rates and flame structure of the cocrystals were found to closely match those of their respective physical mixtures when smaller particle sizes were used (approx. less than 100 um). The results obtained demonstrate that the deflagration behavior of the coformers is not indicative of the deflagration behavior of the resulting physical mixture or cocrystal. However, changes in the resulting flame structure greatly affect the burning rate.</p><p><br></p><p>Next, PLIF of nitric oxide (NO) was utilized to characterize the near surface flame structure of composite propellants of AP and hydroxyl-terminated polybutadiene (HTPB) containing varying particle sizes of AP burning at 1 atm in air. In all propellants, the NO PLIF signal was strongest close to the burning propellant surface and fell to a non-zero constant value within ~1 mm of the surface where it remained throughout the remainder of the flame. Distinct diffusion-flame-like structure was observed above large individual burning AP particles in the propellant containing a bimodal distribution of 400 and 40 um AP. In contrast, the flame of a propellant containing only fine AP (40 um) behaved like a homogeneous, premixed flame. The flame of the propellant containing a bimodal distribution of 200 and 40 um AP also showed similar behavior to a premixed flame with some heterogeneous structure indicating that, at this pressure, the propellant is approaching a limit where the particle sizing is small enough that the flame behaves like a homogeneous, premixed flame. Additionally, propellants containing aluminum were tested. No significant differences were observed in the NO PLIF behavior between the propellants with and without aluminum suggesting that, at these conditions, the aluminum does not have a significant effect on the AP/HTPB flame structure near the burning surface.</p><p><br></p><p>The effect of aluminum particle size on the temperature of aluminized-composite-propellant flames burning at 1 atm is also presented. In this work, measurements of 1) the temperature of CO (within the flame bath gas) and 2) the temperature of AlO (located primarily within regions surrounding the burning aluminum particles) within aluminized, AP-HTPB-propellant flames were performed as a function of height above the burning propellant surface. Three aluminized propellants with varying aluminum particle size (nominally 31 um, 4.5 um, or 80 nm) and one non-aluminized AP-HTPB propellant were studied while burning in air at 1 atm. A wavelength-modulation-spectroscopy (WMS) diagnostic was utilized to measure temperature and mole fraction of CO via mid-infrared wavelengths and a conventional AlO emission-spectroscopy technique was utilized to measure the temperature of AlO. The bath-gas temperature varied significantly between propellants, particularly within 2 cm of the burning surface. The propellant with the smallest particles (nano-scale aluminum) had the highest average temperatures and far less variation with measurement location. At all measurement locations, the average bath-gas temperature increased as the initial particle size of aluminum in the propellant decreased, likely due to increased aluminum combustion. The results support arguments that larger aluminum particles can act as a heat sink near the propellant surface and require more time and space to ignite and burn completely. On a time-averaged basis, the temperatures measured from AlO and CO agreed within uncertainty at near 2650 K in the nano-aluminum propellant flame, however, AlO temperatures often exceeded CO temperatures by ~250 to 800 K in the micron-aluminum propellant flames. This result suggests that in the flames studied here, and on a time-averaged basis, the micron-aluminum particles burn in the diffusion-controlled combustion regime, whereas the nano-aluminum particles burn within or very close to the kinetically controlled combustion regime.</p><p><br></p><p>The study of the effect of aluminum particle size on the temperature of aluminized, composite-propellant flames was then extended to characterize the same propellants burning at elevated pressures ranging from 1 to 10 atm. A novel mid-infrared scanned-wavelength direct absorption technique was developed to acquire measurements of temperature and CO in particle-laden propellant flames burning at up to 10 atm. The results from the application of this diagnostic are among the very first measurements of gas properties in aluminized composite propellant flames burning at pressures above atmospheric pressure. In all propellants, the flame temperature and combustion efficiency of the propellant flames increased with an increase in pressure. In addition, the propellants with smaller aluminum particle sizes achieved higher flame temperatures as the particles were able to ignite and react faster. However, the propellants containing nano-scale and the smallest micron-scale aluminum powders had similar global flame temperatures suggesting that at some point a decrease in particle size results in minimal gains in the overall flame temperature. The results demonstrate how well measurements of gas properties can be used to understand the behavior of the aluminum particle combustion in the flame.</p><p><br></p><p>Last, the design, development, and application of a laser-absorption-spectroscopy diagnostic capable of providing quantitative, time-resolved measurements of gas temperature and HCl concentration in flames of aluminized, composite propellant flames is presented. This diagnostic utilizes a quantum-well distributed-feedback tunable diode laser emitting near 3.27 um to measure the absorbance spectra of one or two adjacent HCl lines using a scanned-WMS technique which is insensitive to non-absorbing transmission losses caused by metal particulates in the flame. This diagnostic was applied to characterize the spatial and temporal evolution of temperature and/or HCl mole fraction in small-scale flames of AP-HTPB composite propellants containing either an aluminum-lithium alloy or micron-scale aluminum. Experiments were conducted at 1 and 10 atm. At both pressures, the flame temperature of the aluminum-lithium propellant, on a time-averaged basis, was 80 to 200 K higher than that of the aluminum-propellant (depending on location in the flame) indicating more complete combustion. In addition, the mole fraction of HCl in the aluminum-lithium propellant flame reached values 65-70% lower than the conventional aluminum-propellant flame at the highest measurement location in the flame. The measurements at both pressures showed similar trends in the reduction of HCl in the aluminum-lithium propellant flame but at 10 atm this occurred on a length scale an order of magnitude smaller than the flame at atmospheric pressure. The results presented further support that the use of an aluminum-lithium alloy is effective at reducing HCl produced by the propellant flame without compromising performance, thereby making it an attractive additive for solid rocket propellants.</p>