Ce travail de thèse porte sur la conception et la réalisation de méta-structures pour l’amelioration des performances de détecteurs dans les gammes spectrales du moyen infrarouge et du térahertz (THz). Ces méta-structures sont des matrices de résonateurs métalliques qui actent aussi comme antennes, permettant une meilleure collection des photons et un plus fort confinement du champ électrique. Dans ce manuscrit, j’examine les résultats expérimentaux concernant deux photo-detecteurs infrarouges à puits quantiques (QWIP) résonants à une longueur d'onde de 55.5 µm (5.4 THz) et de 8.6 µm, implémentés dans des réseaux d’antennes patch. La responsivité, la détectivité et les performances thermiques des dispositifs en microcavité sont systématiquement comparées au même détecteur fabriqué en géométrie standard ‘mesa’, pour lequel le rayonnement infrarouge est couplé par le substrat. La cohérence du modèle est évaluée en comparant le gain photoconducteur de chaque structure QWIP. Dans le moyen infrarouge, le fonctionnement à température ambiante avec une source de radiation thermique est démontré pour la première fois. De plus, en exploitant la courte durée de vie des porteurs dans la zone de QWIP, une détection hétérodyne à température ambiante a été démontrée jusqu’aux fréquences de quelques GHz, limitée uniquement par la fréquence de coupure du circuit externe. Dans la dernière partie de ce manuscrit, plusieurs perspectives sont discutées concernant des structures de détecteurs quantiques couplés à la géométrie de résonateurs patch et des architectures inspirées des métamateriaux, avec la perspective d’améliorer davantage les performances des photodétécteurs / The present thesis manuscript is about the conception and the realisation of metastructures for the improvement of detector performances in the mid-infrared and terahertz (THz) spectral ranges. These meta-structures are arrays of metal resonators that also act as antennas, allowing a better collection of photons and a stronger confinement of the electric field. In this manuscript, I examine the experimental results regarding a 55.5 µm (5.4 THz) and a 8.6 µm quantum well infrared photodetectors (QWIP), implemented into patch-antennae arrays. The responsivity, the specific detectivity and the thermal performances of the antenna-coupled devices are systematically compared to the same detector processed in standard substrate-coupled ‘mesa’ geometry. In the mid-infrared, the room temperature operation using a thermal radiation source is reported for the first time. Moreover, exploiting the short carrier lifetime in semiconductor quantum wells, a room temperature heterodyne detection is demonstrated, at frequencies up to few GHz, limited only by the cut-off frequency of the external circuit. In the last part of this work, several perspectives are discussed, regarding alternative quantum detector structures coupled to the patch resonators geometry and innovative circuit-like plasmonic architectures, envisioning orders of magnitude improvement in photodetector performances

Dans le domaine de la photodétection infrarouge (IR) haute performance refroidie, le photodétecteur à superréseaux (SR) InAs/GaSb est une filière émergente qui peut compléter les technologies déjà établies. Grâce à des années de recherche, l'Institut d'Electronique du Sud (IES) de l'Université de Montpellier a développé une expertise sur la croissance du matériau SR InAs/GaSb par épitaxie par jets moléculaires et sur la fabrication technologique des photodiodes pin dont les performances sont à l'état de l'art mondial dans le moyen IR (3-5µm). Au cours de cette thèse, nous avons étudié deux périodes différentes de SR comme zone active de photodiodes pin ayant une longueur d'onde de coupure à 5 µm à 80K : une riche en InAs (InAs-rich) et l'autre riche en GaSb (GaSb-rich). Ces structures SR présentent des caractéristiques électriques et électro-optiques très différentes. Notamment, les densités de courant de la structure InAs-rich sont très bonnes, de l'ordre de 10-8A/cm2 à 80K, alors que celles de la structure GaSb-rich sont deux décades plus élevées. L'objectif de cette thèse était donc d'analyser les performances de ces photodiodes. Pour cela, nous avons développé une méthode de simulation avec l'outil TCAD SILVACO. Appliquée tout d'abord aux structures InAs-rich, nous avons mis en évidence que ces diodes sont limitées à basse température (typiquement < 120K) par le courant de génération-recombinaison et/ou par le courant tunnel assisté par pièges. La durée de vie extraite de la simulation suit une variation en T-1/2, démontrant que les mécanismes limitant les photodiodes est la génération-recombinaison SRH. Appliquée aux structures GaSb-rich, l'approche SILVACO ne peut expliquer les résultats en courant. Nous démontrons que ces résultats sont fortement liés à la présence du champ électrique dans la zone d'absorption du composant. Cela génère à faible polarisation, un fort courant tunnel, au travers des états Wannier-Stark localisés, qui pénalise fortement le courant d'obscurité et cela malgré des améliorations obtenues au niveau du matériau. Pour finir, nous établissons des règles de dimensionnement de structures à barrière et nous proposons une structure à SR pour le lointain infrarouge. / Among the high performance cooled infrared (IR) photodetector systems, the InAs/GaSb superlattice (SL) is an emerging material which may complement the currently technologies already established. Over the last 10 years, the Institut d'Electronique du Sud (IES) of the University of Montpellier has developed skills in both the growth of SL materials by molecular beam epitaxy and the process fabrication of pin photodiodes. The photodiode fabricated by the IES group are at the state of the art in the mid IR (3 – 5 μm). During this thesis, we studied two structures with different SL periods for the pin active zone showing the same cut-off wavelength of 5 μm at 80K: the structure called InAs-rich structure presents InAs layer thicker than the GaSb layer in each SL period while this configuration is reversed in the case of the GaSb-rich structure. These SL structures have very different electrical and electro-optical characteristics. In particular, the current densities of the InAs-rich structure are very good, about 10-8 A/cm2 at 80K - two orders of magnitude greater than that of GaSb-rich. The aim of this thesis work was therefore to analyze the performance of these photodiodes. For this purpose, we developed a simulation method with the SILVACO TCAD tool. Using this tool, we found that the InAs-rich diodes are limited at low temperatures (typically under 120K) by generation recombination and/or by assisted tunneling currents. The lifetimes extracted from the simulation follows the T-1/2 law, which demonstrates that the limiting mechanism is SRH recombination. However, we found that we could not study the current densities of the GaSb-rich structure using the same procedure. We demonstrate that these results are strongly related to the presence of the electric field in the absorption zone of the device. This electric field generates, at low biases, a strong tunneling current through localized Wannier-Stark states, which strongly limits the overall current despite material improvements. Finally, we define the design conditions to achieve an optimized SL barrier structure and propose a design for SL structures targeting the long wavelength domain.

We present a detailed study of mid-infrared spectroscopy and optical imaging of Seyfert galaxies with the goal of understanding the properties of astronomical dust around the central supermassive black hole and the accretion disk. Specifically, we have studied Spitzer Space Telescope mid-infrared spectra of 12 Seyfert 1.8-1.9s and 58 Seyfert 1s and 2s available in the Spitzer public archive, and the nuclear dust morphology in the central 500 pc of 91 narrow and broad-line Seyfert 1s using optical images from the Hubble Space Telescope. We have also developed visualization software to aid the understanding of the geometry of the central engine. Based on these studies, we conclude that the nuclear regions of Seyfert galaxies are fueled by dusty spirals driven by the large-scale stellar bars in the host galaxy. The accumulation of dusty gas in the central kiloparsec leads to enhanced star formation. In this case, the circumnuclear starburst and the central engine compete for dominance in the heating of the circumnuclear dust. Emission from the heated dust is most clearly seen in the mid-infrared. We find that the spectra of Seyfert 2s show the most variety in the continuum shapes due to different starburst contributions. We find that the spectra of Seyfert 2s that are devoid of starburst contribution are dominated by a single thermal component at a temperature of T ~ 170 K. We also find that the mid-IR continua of Seyfert 1.8/1.9 galaxies are more like those of starburst-dominated Seyfert 2s than Seyfert 1s, contrary to expectations. We discuss the implications of these findings in the context of the Unified Model of AGN and the secular evolution of Seyfert nuclei.

Part I: Successful transition of polymer coated, ATR-FTIR sensor devices from a laboratory environment to real world field applications for detecting and quantifying VOCs in water is shown. Simultaneous, quantitative detection of BTX mixtures in water during enrichment into polymer coated ZnSe ATR elements has been performed. The obtained results showed accurate detection and quantification to the low ppb concentration region. Fiber-optic evanescent field measurement campaigns have been conducted at simulated field conditions during which concentration gradients of various VOCs in the mg/L range have been monitored successfully. The first test of an ATR based, polymer coated sensor system under real world field conditions, the chlorobenzene concentration in groundwater at mg/L levels was determined. An interesting aspect of these measurements was the experimental proof for the dependence of analyte extraction dynamics on the flow conditions of the sample matrix surrounding the extractive polymer membrane. The obtained results demonstrate that MIR evanescent field sensors are suitable for in-situ analysis at real world field conditions for environmental monitoring applications. PART II: Recently, measurements of disturbed soils have shown different spectral contrast in comparison to undisturbed soils. In this work first measurements at controlled laboratory conditions have been performed to investigate individual minerals of the soil matrix and their spectral characteristics under various environmental conditions. ATR spectroscopy has been applied to investigate multi-disperse quartz sand and mono-disperse soda lime glass spheres samples. For the investigation of spectral differences between pristine and disturbed quartz sand, a wetting/drying procedure with subsequent sample aerating has been developed. In addition to established differences in spectral contrast of disturbed and undisturbed soil, a strong spectral shift of absorption features was observed. When probed with s- or p-polarized light, both samples showed strong LO-TO mode splitting. The studies also reveal that the main reason for spectral differences of pristine and disturbed soils is caused by water facilitated changes of the particle size distribution in the probed volume. The presented results advance the variety of spectral characteristics useful for the detection of disturbed soils (i.e. possible landmine sites) with MIR imaging systems.

Wavelength-tunable optical response from solid-state optoelectronic devices is a desired feature for a variety of applications such as spectroscopy, laser emission tuning, and telecommunications. Nonlinear optical response, on the other hand, has an important role in modern photonic functionalities, including efficient frequency conversions, all-optical signal processing, and ultrafast switching. This study presents the development of optical devices with wavelength tunable or nonlinear optical functionality based on plasmonic effects. For the first part of this study, widely wavelength tunable optical bandpass filters based on the unique properties of long-range surface plasmon polaritons (LR SPP) are presented. Planar metal stripe waveguides surrounded by two different cladding layers that have dissimilar refractive index dispersions were used to develop a wide wavelength tuning. The concept was demonstrated using a set of index-matching fluids and over 200nm of wavelength tuning was achieved with only 0.004 of index variation. For practical application of the proposed concept, a thermo-optic polymer was used to develop a widely tunable thermo-optic bandpass filter and over 220 nm of wavelength tuning was achieved with only 8 ºC of temperature variation. Another novel approach to produce a widely wavelength tunable optical response for free-space optical applications involves integrating plasmonic metasurfaces with quantum-electronic engineered semiconductor layers for giant electro-optic effect, which is proposed and experimentally demonstrated in the second part of this study. Coupling of surface plasmon modes formed by plasmonic nanoresonators with Stark tunable intersubband transitions in multi-quantum well structures induced by applying bias voltages through the semiconductor layer was used to develop tunable spectral responses in the mid-infrared range. Experimentally, over 310 nm of spectral peak tuning around 7 μm of wavelength with 10 ns response time was achieved. As the final part of this study, highly nonlinear metasurfaces based on coupling of electromagnetically engineered plasmonic nanoresonators with quantum-engineered intersubband nonlinearities are proposed and experimentally demonstrated. In the proof-of-concept demonstration, an effective nonlinear susceptibility over 50 nm/V was measured and, after further optimization, over 480 nm/V was measured for second harmonic generation under normal incidence. The proposed concept shows that it is possible to engineer virtually any element of the nonlinear susceptibility tensor of the nonlinear metasurface. / text

Nonlinear optical interaction in quasi-phase-matched structures opens up unique possibilities to build compact and efficient parametric devices such as optical parametric oscillators, generators, and amplifiers with tailored spectral properties. The focus of this thesis is on novel parametric interactions with periodically-poled KTiOPO4 (PPKTP) as the parametric gain medium. Optical parametric oscillators (OPOs) are attractive light sources for many applications, particularly in spectroscopy, and plays a central role in this thesis. Special attention is put on simple, yet powerful, spectral-manipulation and bandwidth-narrowing techniques for OPOs. The overall knowledge gained from these studies has been used for device construction of several tunable ultraviolet sources for biological sensing. In the case of bandwidth narrowing, the observation of decreasing spectral bandwidth in a noncollinear, idler-resonant OPO, as compared with a signal-resonant one, has been found to be due to the interplay between the material properties and the angular dispersion of PPKTP. To further reduce the bandwidth, we have shown that it is very beneficial to replace the output mirror in an OPO with a bulk Bragg grating. In fact, even close to degeneracy, where the bandwidth is typically wide, this approach is able to decrease the bandwidth drastically. Moreover, different OPO cavity designs have been examined in order to spectrally manipulate the resonant waves. By deploying a grating in a ring OPO cavity, it becomes possible to access the resonant wave and spectrally manipulated it in a zero-dispersion arrangement; the filtered wave is subsequently sent back into its own cavity as a seed signal, in a self-seeding arrangement. This particular cavity design decreases the bandwidth close to ~ 1000 times as compare to the free-running mode. An interesting phenomenon arises when two mutually coherent laser beams are used to pump a linear OPO cavity. When the pump beams intersect within the PPKTP crystal, an interference grating is formed and acts as a catalyst for the generation of new spectral sidebands through multiple cascaded four-wave mixing, in the pump, the idler and the signal directions. The spacing of these sidebands is determined geometrically by the incident pump angle, while the signals are continuously tunable over the c-band telecom window (λ ~ 1.5 μm) by rotating the cavity. Ultrabroad bandwidths have been generated in an optical parametric generator (OPG) pumped by an amplified picosecond Ti:sapphire laser. In the collinear direction the output spectrum extends over three octaves in the mid-infrared region. This enormously broad spectrum is also Fourier-filtered and subsequently used for narrowband seeding of an optical parametric amplifier (OPA). Finally, the spectral range between 285 nm and 340 nm is of importance for detection of biological substances through fluorescence spectroscopy. With this spectral region in mind a practical way to generate a tunable parametric device in the ultraviolet region is presented in the thesis. The developed ultraviolet laser is used for studies of the characteristics of biological particles. The ultraviolet source and the results from these studies, will be utilized in an integrated detection system, a so called early-warning system. / QC 20100923

Thesis (MSc Food Sc)--University of Stellenbosch, 2011. / ENGLISH ABSTRACT: Near infrared hyperspectral imaging (NIR HSI) in conjunction with multivariate image analysis was evaluated for the detection of millet and buckwheat flour in ground black pepper. Additionally, midinfrared (MIR) spectroscopy was used for the quantification of millet and buckwheat flour in ground black pepper. These techniques were applied as they allow non-destructive, invasive and rapid analysis. Black pepper and adulterant (either millet or buckwheat flour) mixtures were made in 5% (w/w) increments spanning the range 0-100% (w/w). The mixtures were transferred to eppendorf tube holders and imaged with a sisuChema short wave infrared (SWIR) pushbroom imaging system across the spectral range of 1000–2498 nm. Principal component analysis (PCA) was applied to pseudo-absorbance images for the removal of unwanted data (e.g. background, shading effects and bad pixels). PCA was subsequently applied to the ‘cleaned’ data. An adulterant concentration related gradient was observed in principal component one (PC1) and a difference between black pepper adulterated with buckwheat and millet was noted in PC4. Four absorption peaks (1461, 2241, 2303 and 2347 nm) were identified in the loading line plot of PC1 that are associated with protein and oil. The loading line plot of PC4 revealed absorption peaks at 1955, 1999, 2136 and 2303 nm, that are related to protein and oil. Partial least squares discriminant analysis (PLS-DA) was applied to NIR HSI images for discrimination between black pepper adulterated with varying amounts of adulterant (millet or buckwheat). The model created with millet adulterated black pepper samples had a classification accuracy of 77%; a classification accuracy of 70% was obtained for the buckwheat adulterated black pepper samples. An average spectrum was calculated for each sample in the NIR HSI images and the resultant spectra were used for the quantification of adulterant (millet or buckwheat) in ground black pepper. All samples were also analysed using an attenuated total reflectance (ATR) Fourier transform (FT) – infrared (IR) instrument and MIR spectra were collected between 576 and 3999 cm-1. PLS regression was employed. NIR based predictions (r2 = 0.99, RMSEP = 3.02% (w/w), PLS factor = 4) were more accurate than MIR based predictions (r2 = 0.56, RMSEP = 19.94% (w/w), PLS factors = 7). Preprocessed NIR spectra revealed adulterant specific absorption bands (1743, 2112 and 2167 nm) whereas preprocessed MIR spectra revealed a buckwheat specific signal at 1574 cm-1. NIR HSI has great promise for both the qualitative and quantitative analysis of powdered food products. Our study signals the beginning of incorporating hyperspectral imaging in the analysis of powdered food substances and results can be improved with advances in instrumental development and better sample preparation. / AFRIKAANSE OPSOMMING: Die gebruik van naby infrarooi hiperspektrale beelding (NIR HB) tesame met veelvoudige beeldanalise is ondersoek vir die opsporing van stysel-verwante produkte (giers en bokwiet) in gemaalde swart pepper. Middel-infrarooi (MIR) spektroskopie is addisioneel gebruik vir die kwantifisering van hierdie stysel-verwante produkte in swart pepper. Albei hierdie tegnieke is toegepas aangesien dit deurdringend van aard is en dit bied nie-destruktiewe sowel as spoedige analise. Swart pepper en vervalsingsmiddel (giers of bokwiet) mengsels is uitgevoer in 5% (m/m) inkremente tussen 0 en 100% (m/m). Eppendorfbuishouers is met die mengsels gevul en hiperspektrale beelde is verkry deur die gebruik van ‘n sisuChema SWIR (kortgolf infrarooi) kamera met ‘n spektrale reikwydte van 1000–2498 nm. Hoofkomponent-analise (HK) is toegepas op pseudo-absorbansie beelde vir die verwydering van ongewenste data (bv. agtergrond, skadu en dooie piksels). Hoofkomponent-analise is vervolgens toegepas op die ‘skoon’ data. Hoofkomponent (HK) een (HK1) het die aanwesigheid van ‘n vervalsingsmiddel konsentrasie verwante gradient getoon terwyl HK4 ‘n verskil getoon het tussen swart pepper vervals met giers en bokwiet. Vier absorpsiepieke (1461, 2241, 2303 en 2347 nm) was geïdentifiseer binne die HK lading stip van HK1 wat met proteïen en olie geassosieer kon word. Die HK lading stip van HK4 het absorpsipieke by 1955, 1999, 2136 en 2303 nm aangedui wat verband hou met proteïen en olie. Parsiële kleinste waarde diskriminant-analise (PKW-DA) is toegepas op die hiperspektrale beelde vir die moontlike onderskeiding tussen swart pepper vervals met verskeie hoeveelhede vervalsingsmiddel (giers of bokwiet). ‘n Klassifikasie koers van 77% is verkry vir die model ontwikkel met giers vervalsde swart pepper terwyl die model ontwikkel met bokwiet vervalsde swarte pepper ‘n klassifikasie koers van 70% bereik het. ‘n Gemiddelde spektrum is bereken vir elke monster in die hiperspektrale beelde en die resulterende spektra is gebruik vir die kwantifisering van vervalsingsmiddels (giers of bokwiet) in gemaalde swart pepper. ‘n ATR FT-IR instrument met spektrale reikwydte van 576-3999 cm-1 is additioneel gebruik vir die analise van alle monsters. Parsiële kleinste waarde regressie is gebruik vir kwantifikasie doeleindes. NIR gebasseerde voorspellings (r2 = 0.99, RMSEP = 3.02% (m/m), PLS faktore = 4) was meer akkuraat as die MIR gebasseerde voorspellings (r2 = 0.56, RMSEP = 19.94% (m/m), PLS faktore = 7). Vooraf behandelde NIR spektra het vervalsingsmiddel verwante absorpsiepieke (1743, 2112 en 2167 nm) aangetoon terwyl vooraf behandelde MIR spektra ‘n bokwiet verwante absorpsiepiek by 1574 cm-1 aangedui het. NIR HB toon goeie potensiaal vir beide kwalitatiewe en kwantitatiewe analise van gepoeierde voedsel produkte. Ons studie kan gesien word as die begin van die inkorporasie van hiperspektrale beelding in die analise van gepoeierde voedsel material en verbeterde resulte kan verkry word deur die vordering in instrumentasie ontwikkeling en verbeterde monstervoorbereiding.

Les lasers à cascade quantiques (LCQ) sont des sources puissantes de rayonnement térahertz (THz) et moyen infrarouge (MIR). Elles reposent sur une transition intersousbande dans la bande de conduction des nanostructures semiconductrices constituant le LCQ. Ce travail de thèse présente une étude fondamentale de l'optique non-linéaire résonante dans les LCQ. La génération de mélange de fréquences entre un LCQ THz ou MIR et un faisceau proche infrarouge (NIR) est démontrée dans la cavité même du LCQ. Les non-linéarités des puits quantiques constituant la zone active du LCQ sont exaltées grâce à une excitation NIR résonante avec les transitions interbandes et grâce au photon du LCQ résonant avec les transitions intersousbandes de la structure. Ces excitations résonantes entrainent une forte exaltation de la susceptibilité non-linéaire, permettant une interaction efficace sans considération pour l'accord de phase. De précédentes études limitées aux températures cryogéniques, ont mis en évidence le mélange d'ondes résonant entre un LCQ THz basé sur GaAs et un faisceau NIR à 800 nm. Le travail novateur de cette thèse montre que le mélange d'ondes résonant dans les LCQ peut être étendu à la gamme des LCQ MIR et à des excitations de pompe dans le domaine télécom, à température ambiante. De plus, les limites liées à l'absorption sous excitation résonante ont été en partie dépassées, grâce à une géométrie en réflexion. Ce travail a permis une compréhension approfondie des non-linéarités interbandes et intersousbandes résonantes dans les LCQ, ouvrant la voie vers des applications potentielles telles que le décalage de longueurs d'ondes tout-optique pour les télécommunications. / Quantum cascade lasers (QCLs) are powerful terahertz (THz) and mid-infrared (MIR) sources. Their emission relies on intersubband transitions i.e. transitions between confined electronic states in the conduction band of these semiconductor nanostructure-based lasers.This PhD thesis presents a fundamental study of resonant nonlinear optics in QCLs. Nonlinear frequency mixing between a THz or MIR QCL photon and a near infrared (NIR) pump has been shown within the QCL cavity. Nonlinearities from the QCL active region, composed of a set of quantum wells, can be enhanced owing to a NIR excitation that is resonance with interband transitions, and with the QCL photon in resonance with intersubband transitions. These resonant excitations permit a strong exaltation of the nonlinear susceptibility, allowing an efficient interaction without considerations of phase matching. Previous studies, limited to cryogenic temperatures, have shown nonlinear frequency mixing between a GaAs based THz QCL and an 800 nm NIR beam.This thesis presents an original work highlighting that resonant nonlinear optics in QCLs can be extended to the MIR, and to telecom range pump excitations, at room temperature. Furthermore, previously limits related to absorption at resonant excitations have also been partially overcome, by proposing a geometry in reflection.As well as proving an in-depth understanding of interband and intersubband nonlinearities in QCLs, this work paves the way to potential applications such as all optical wavelength shifting for telecommunications, and the up-conversion of THz and MIR photons into thetechnologically mature NIR range.

La détection hétérodyne infrarouge est une technique qui a été développée principalement pour améliorer la détectivité des détecteurs infrarouges, en particulier dans la fenêtre 8-12 μm. Cette technique a longtemps été étroitement associée à l’usage de lasers à gaz. Les domaines d’applications ont été principalement les études astrophysiques et atmosphériques. Peu d’autres applications ont pu être envisagées du fait de la complexité de mise en oeuvre et de l’encombrement de ce type d’instruments. Les progrès récents dans le domaine des lasers à semi-conducteurs (les lasers à cascade quantique - QCL - couvrent une grande partie du spectre infrarouge) permettent d’envisager de nouveaux développements et de nouvelles applications pour la détection hétérodyne infrarouge, par exemple pour la détection et l’identification à distance de molécules d’intérêt atmosphérique telles que les polluants. Les principaux atouts de la détection hétérodyne concernent la sélectivité spectrale et directionnelle de l’instrument. Elle est applicable dans le domaine civil aux molécules d’intérêt atmosphérique telles que l’ozone et le dioxyde de carbone et pour le domaine militaire à la détection d’espèces dangereuses. Un récepteur hétérodyne a été réalisé avec un QCL émettant autour de 10 μm et un corps noir stabilisé en température. Dans ce but, plusieurs systèmes ont été envisagés : un système à base de lentilles, un autre à base de miroirs paraboliques hors axes et un dernier à base de fibres optiques moyen infrarouge. Parallèlement, un héliostat a aussi été développé dans le but de réaliser des mesures atmosphériques. / Infrared heterodyne sensing is a technique which has been developed primarily toimprove the detectivity of infrared detectors, particularly in the 8 − 12 μm window. This technique has long been closely associated with the use of gas lasers. The fields of application were mainly astrophysical and atmospheric studies. Due to the complexity of implementation and the size of this type of instrument, ew other applications could have been envisaged. Recent progress in the field of semiconductor lasers (Quantum Cascade Laser - QCL - cover a large part of the infrared spectrum) enable to consider new developments and new applications for infrared heterodyne sensing, for example for the remote detection and identification of atmospheric molecules, such as pollutants. The main advantages of heterodyne sensing concern spectral and directional selectivity of the instrument. It is applicable in civil sector to atmospheric molecules such as ozone and carbon dioxide, and for the military one to detect hazardous species. A heterodyne receiver has been developed with a QCL emitting at around 10 μm and a temperature stabilized black body. To this end, several systems were considered: a system based on lens, another one based on off-axis parabolic mirrors and a last one based on mid-infrared optical fibers. Meanwhile, a heliostat has also been developed in order to do atmospheric measurements.

Des fibres optiques en verres de chalcogénure transmettant dans le moyen infrarouge (MIR) ont été développées par le laboratoire Verres et Céramiques de l’université de Rennes 1. Des travaux ont ensuite montré les potentialités de ces fibres comme outil diagnostic pour la spectroscopie MIR appliquée aux biofluides. Le spectre moyen infrarouge d’un échantillon complexe est le reflet de sa composition moléculaire qui, lorsque celui-ci est un biofluide, peut être assimilé à une image métabolique instantanée d’un individu. Cette technique constitue donc un outil intéressant pour le diagnostic médical. La société Diafir fut crée à la suite du programme ANR émergence FIR-MED pour développer les potentialités de la spectroscopie par fibre optique. L’objectif de l’entreprise est de développer un système composé d’un spectromètre spécifiquement adapté au capteur à fibre optique et d’un algorithme associé pour une réponse diagnostique ne nécessitant pas de connaissance particulière en spectroscopie infrarouge. Dans le cadre de ces travaux de thèse associant l’IRDL et la société Diafir, des projets variés d’applications médicales de la technologie ont été abordés avec pour objectif de développer une méthodologie d’analyse des spectres MIR. Pour cela, il a été nécessaire dans un premier temps de caractériser le signal obtenu à partir des capteurs et d’optimiser et valider des protocoles de mesure applicables aux différents biofluides de manière à réduire au mieux les sources de variabilité d’ordre physique et environnemental. La construction d’un diagnostic médical à partir de spectres infrarouge qui sont des données en grande dimension implique de sélectionner un petit nombre de variables spectrales explicatives. Des méthodes de sélection de variables ont été sélectionnées afin d’éviter l’effet « boite noire » en établissant le lien avec les fonctions biochimiques impactées par les pathologies. Cette approche spectrale infrarouge a notamment permis de mettre en évidence, au cours du développement de pathologies, l’existence de transitions a priori non détectées par les dosages biochimiques classiques. / Chalcogenide glass optical fibres exhibiting unique properties of mid-infrared (MIR) transparency have been developed by the Laboratoire Verres et Céramiques of Rennes 1 University. Our studies investigate the potential of such fibres as a tool for MIR spectroscopy applied to biofluids based diagnostic. The MIR spectrum of complex samples features its molecular composition which, when a biofluid is considered, can be assimilate to an instant metabolic imaging of an individual. The Diafir Company was created following the ANR emergence FIR-MED program to develop the potential of optical fibre biomedical spectroscopy. The company's goal is to develop a system that is composed of the optical fibre sensor, a spectrometer specifically designed to these sensors and an associated algorithm for a diagnostic response without specific knowledge of infrared spectroscopy. As part of this thesis work, linking the IRDL and the Diafir Company, various projects of biomedical applications were driven with the aim of developing a MIR spectra analysis methodology. Accordingly, it was necessary initially to characterize the signal obtained from the sensors and to optimize and validate robust measurement protocols for each biofluid tested with the aim to reduce the physical and environmental sources of variability. The medical diagnosis construction from infrared spectra, that are high dimensional data, involves selecting from the whole spectral data set a small number of explanatory variables. Purposely, particular variables selection algorithms were selected to avoid the effect of "black box" by establishing the link with the biochemical functions affected by the disease. This infrared spectral approach allowed identifying previously unrevealed transitions in the time course of pathologies which were not detected from conventional biochemical markers