Quantum Cascade Laser-Based Photoacoustic Spectroscopy for Trace Vapor Detection and Molecular Discrimination

We report on the development of a microelectromechanical systems (MEMS)-scale photoacoustic sensor for the detection of trace gases. A mid-infrared quantum cascade laser (QCL) was used to determine detection limits for acetic acid, acetone, 1,4-dioxane, and vinyl acetate. The source was continuously tunable from 1015 cm−1 to 1240 cm−1, allowing for the collection of photoacoustic vibrational spectra for these gases. Exceptional agreement between the measured photoacoustic spectra and the infrared spectra for acetic acid, acetone, 1,4-dioxane, and vinyl acetate was observed. Partial least-squares (PLS) regression was used to develop an algorithm for classification of these compounds based solely on photoacoustic spectra

Phase-shift Cavity Ring Down Spectroscopy Set-up for NO2 Sensing : Design and Fabrication

An indigenously designed cavity ring down spectroscopy cell of 80 cm length of mild steel material was fabricated by attaching two 1″ diameter high reflecting concave mirrors with reflectivity 99.997 % at 405 nm and radius of curvature was 1 m in specially designed mirror holding assemblies to the cell at two ends. Fine alignment of the resonator is facilitated with three tip-tilt adjusting screws to the mirror-mounting plate assembly. The PS-CRDS experimental set-up is evaluated by measuring the phase shift values corresponding to the absorption of NO2 gas filled at low pressures in the cell. The limit of detection of pure NO2 using the set-up under given conditions of Ar @ 50 mbar is estimated to be 1.50 × 1011 cm-3 and @ 60 mbar as 2 × 1011 cm-3.Defence Science Journal, Vol. 65, No. 1, January 2015, pp.25-30, DOI:http://dx.doi.org/10.14429/dsj.65.779

Incorporating nanomaterials with MEMS devices.

This dissertation demonstrates an elegant method, known as \u27micro-origami\u27 or strain architecture to design and fabricate three-dimensional MEMS structures which are assembled using actuation of a metal-oxide bilayer with conventional planar lithography. Folding allows creating complex, robust, three-dimensional shapes from two-dimensional material simply by choosing folds in the right order and orientation, small disturbances of the initial shape may also be used to produce different final shapes. These are referred to as pop-up structures in this work. The scope of this work presented the deposition of colloidal gold nanoparticles (GNPs) into conformal thin films using a microstenciling technique. Results illustrated that the gold nanoparticle deposition process can easily be integrated into current MEMS microfabrication processes. Thin films of GNPs deposited onto the surfaces of siliconbased bistable MEMS and test devices were shown to have a significant effect on the heating up of microstructures that cause them to fold. The dissertation consists of four chapters, covering details of fabrication methods, theoretical simulations, experimental work, and existing and potential applications. Chapter II illustrates how control of the folding order can generate complex three-dimensional objects from metal-oxide bilayers using this approach. By relying on the fact that narrower structures are released from the substrate first, it is possible to create multiaxis loops and interlinked objects with several sequential release steps, using a single photomask. The structures remain planar until released by dry silicon etching, making it possible to integrate them with other MEMS and microelectronic devices early in the process. Chapter III depicts the fabrication process of different types of bistable structures. It describes the principle of functioning of such structures, and simulations using CoventorWare are used to support the concept. We talk over about advantages and disadvantages of bistable structures, and discuss possible applications. Chapter IV describes fabrication procedure of nanoparticle-MEMS hybrid device. We introduce a convenient synthesis of GNPs with precisely controlled optical absorption in the NIR region by a single step reaction ofHAuCl4 and Na2S203. We take a look at different techniques to pattern gold nanoparticles on the surface of MEMS structures, and also provide a study of their thermal properties under near IR stimulation. We demonstrate the first approach of laser-driven bistable MEMS actuators for bioapplications. Finally, in Conclusion discuss the contributions of this dissertation, existent limitations and plans of the future work

Quantum Cascade Laser-Based Photoacoustic Spectroscopy for Trace Vapor Detection and Molecular Discrimination

We report on the development of a microelectromechanical systems (MEMS)-scale photoacoustic sensor for the detection of trace gases. A mid-infrared quantum cascade laser (QCL) was used to determine detection limits for acetic acid, acetone, 1,4-dioxane, and vinyl acetate. The source was continuously tunable from 1015 cm-1 to 1240 cm-1, allowing for the collection of photoacoustic vibrational spectra for these gases. Exceptional agreement between the measured photoacoustic spectra and the infrared spectra for acetic acid, acetone, 1,4-dioxane, and vinyl acetate was observed. Partial least-squares (PLS) regression was used to develop an algorithm for classification of these compounds based solely on photoacoustic spectra

Développement de deux instruments LIDAR multi-longueurs d'onde et multi-espèces à base de sources paramétriques

Atmospheric global monitoring and air quality are major environmental concerns. Global monitoring of some trace and green-house gases would help to understand the consequences of human activities on our environment. The aim of this work is to develop two multi-wavelengths and multi-species direct detection lidar instruments, based on the same laser transmitter baseline approach - an innovative parametric source, the Nested Cavity optical parametric oscilator-and to target two applications: the monitoring of air quality on industrial sites and the monitoring of greenhouse gases from space. The first instrument was designed for industrial plant monitoring applications, in the 3.3-3.8µm, and allows the measurement of multi-species mean concentrations along the line of sight, over a range of around a hundred meters. This instrument was implemented for simultaneous measurements of atmospheric methane and water vapour.The second instrument targets the green-house gases measurement from space applications. In this frame, a new multi-wavelengths and multi-species emitter was developed at 2 µm for space applications. We have demonstrated that this new emitter could address three species: carbon dioxide, water vapor and methane, and studied his potential for space-borne applications.. The architecture of a complete range-resolved instrument based on this transmitter was proposed. Moreover, a numerical algorithm was developed to estimate the instrument’s performances with a direct detection scheme.La surveillance globale de l’atmosphère et de la pollution de l’air est devenue un enjeu majeur ces dernières années afin d’estimer les conséquences des activités humaines sur notre environnement. Au cours de ces travaux de thèse, l’objectif a été de développer deux instruments LIDARs en détection directe basés sur des émetteurs multi-longueurs d’onde et multi-espèces mettant en œuvre des sources paramétriques optiques innovantes basées sur la technologie NesCOPO (nested cavity optical parametric oscillator) afin de répondre à deux applications : le suivi de la qualité de l’air sur sites industriels et le suivi des gaz à effet de serre depuis l’espace. Un premier instrument multi-espèces a été développé dans le cadre du suivi de la qualité de l’air sur sites industriels, dans la gamme spectrale 3,3 à 3,8 µm, et dédié à des mesures de concentrations moyennes le long de la ligne de visée pour des portées de l’ordre de la centaine de mètres. Une démonstration du potentiel multi-espèces de l’instrument a été réalisée en mesurant simultanément les concentrations en méthane et en vapeur d’eau atmosphériques. A partir d’une source optique existante dédiée à la mesure du dioxyde de carbone seul, un second émetteur multi-longueurs d’onde et multi-espèces a été développé dans une gamme spectrale autour de 2 µm. Son potentiel pour la mesure des gaz à effets de serre depuis l’espace a été étudié En particulier, nous avons démontré que cet émetteur permet de mesurer trois gaz atmosphériques : CO2, H2O et CH4. Une architecture globale d’instrument intégrant cet émetteur a été proposée, afin de réaliser des mesures résolues spatialement, avec des portées de quelques km. De plus, un code de simulation a été développé pour estimer les performances de cet instrument en détection directe