Le moyen infrarouge est la région spectrale comprise entre 2 et 20 µm. Cette gamme de longueurs d'onde présente un fort intérêt scientifique grâce à la présence des transitions vibrationnelles fondamentales caractéristiques d'espèces moléculaires en phase liquide ou gazeuse. Les capteurs en optique intégrée sont devenus une excellente alternative pour la détection in situ car ils présentent certains avantages sur les autres types de capteurs, tels que l'intégration des éléments dans un dispositif compact. Ils sont capables d'effectuer des détections sélectives et quantitative dans divers domaines sociétaux tels que la santé, la défense et l'environnement. Dans cette thèse, nous présentons la conception, la fabrication et la caractérisation à 7.7 µm d'un transducteur spectroscopique intégré à base de verres de chalcogénures. Des couches à base de Ge-Sb-Se ont été déposées par pulvérisation cathodique RF magnétron. Des guides d'onde de type ridge ont ensuite été mise en forme, par photolithographie et gravure sèche (gravure ionique réactive) avec un plasma de CHF3. Différentes structures ont ainsi pu être réalisées : guides droits, jonctions Y, guide en spirale ou encore guides en S. En outre, la propagation guidée a été observé à 7.7 µm et des pertes de propagation égales à 2.5 dB/cm ont été mesurées à cette longueur d'onde. Enfin, des substances chimiques en phase liquide (isopropanol et acide acétique dissous dans du cyclohexane) ont été détectées par onde évanescente. Des limites de détection égales à 2 %v/v et 0.2 %v/v ont été, respectivement, démontrées à 7.7 µm pour l'isopropanol et l'acide acétique. Enfin, des simulations ont démontré le potentiel de ce capteur intégré pour la détection de substances polluantes contenues dans l'eau ou dans l'air avec des limites de détection inférieures à celles imposées par les normes internationales de l'environnement. L'ensemble de ces résultats représente une première étape prometteuse vers le développement d'applications dans le moyen Infrarouge au sein du laboratoire Foton. / The mid-infrared is a spectral range (2-20 µ m) of great scientific and technological interest. Indeed, the strong vibrational absorption bands of numerous molecules overlap this wavelength range. Thus, the mid-infrared has become in the last years a suitable solution for chemical sensing applications in gas or liquid phase. Furthermore, on-chip sensors provide several advantages over other kind of sensors, such as high integration of elements in a compact device and low fabrication cost by an easy-going to mass production. They could allow quantitative, sensitive and selective detection for health, defense and environmental applications. This thesis presents the design, fabrication and optical characterization at 7.7 µ m of a spectroscopic optical integrated sensor based on chalcogenide glasses. Ge-Sb-Se multilayered structures were deposited by RF magnetron sputtering. Using i-line photolithography and fluorine-based reactive ion etching (RIE-ICP), ridge waveguides were processed as straight waveguide, Y-junction, spiral and S-shape waveguides. Single-mode optical propagation at 7.7 µ m was observed by optical near-field imaging and optical propagation losses of 2.5 dB/cm were measured. Finally, chemical substances in liquid phase (isopropanol - and acetic acid, both dissolved in cyclohexane) were detected at 7.7 µ m by evanescent field. Limits of detection of 2 %v/v and 0.2 %v/v are demonstrated, respectively, for isopropanol and acetic acid. Furthermore, simulations were performed to assess the potential of the optical integrated sensor to achieve limits of detection lower than environmental and health standards for air and water pollutants. These results represent a first promising step towards the development of mid-infrared applications at the Foton laboratory.

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The ability to tune the properties over a wide range of values by changing the additives, composition, etc., has made chalcogenide glassy semiconductors, most interesting from both fundamental physics as well as technology point of view. In particular, the occurrence of the two network topological thresholds namely the Rigidity Percolation Threshold (RPT) and the Chemical Threshold (CT) and their influence on various properties of chalcogenide glasses have been of immense interest during the last three decades. The Rigidity Percolation Threshold (also known as the Stiffness Threshold or Mechanical Threshold) corresponds to the composition at which the material transforms from a floppy polymeric glass to a rigid amorphous solid, whereas at Chemical Threshold the sample tends towards an ordered state. Though the rigidity percolation has been considered for long to occur at a critical threshold defined by the constraint’s theory, the recent theoretical and experimental investigations have found the RPT to occur over a range of compositions. In systems exhibiting an extended rigidity percolation, two distinct transitions namely from a floppy to an isostatically rigid phase and from an isostatically rigid to a stressed rigid phase are seen. In the category of chalcogenide glasses, tellurides have been found to exhibit interesting properties including the phenomenon of electrical switching which finds applications in Phase Change Memories (PCM). Studies on various thermal, electrical and photoelectrical properties of glassy tellurides help us in identifying suitable materials for different technological applications. This thesis deals with Differential Scanning Calorimetric (DSC) & Temperature Modulated Alternating Differential Scanning Calorimetric (ADSC) studies, electrical switching investigations, photoconductivity & photothermal measurements on certain metal doped telluride glasses. The composition dependence of properties such as glass transition & crystallization temperatures, switching voltage, thermal diffusivity, photosensitivity, etc., have been analyzed to obtain information about topological thresholds, thermally reversing window, etc. The first chapter of thesis provides an overview of properties of amorphous semiconductors, in particular chalcogenide glasses. The local & defect structure, the electronic band structure & electrical properties, electrical switching behavior, etc., are discussed in detail. The theoretical aspects related to the experiments undertaken in this thesis work have also been described. The instrumentation used for various experiments conducted to measure thermal, electrical, photoelectrical and photothermal properties have been discussed in chapter two. The chapter three deals with the photocurrent measurements on As40Te60-xInx (7.5 ≤ x ≤ 16.5) glasses. In these samples, it has been found that the photocurrent increases with illumination, which is understood on the basis of the large dielectric constant and also due to the presence of a large number of positively charged defect states. Further, the composition dependence of the conductivity activation energy and the photosensitivity exhibit a maximum at x = 12.5 (<r> = 2.65) and a minimum at x = 15.0 (<r> = 2.70) which has been identified to be the Rigidity Percolation Threshold (RPT) and the Chemical Threshold (CT) respectively. The results of electrical switching, DSC and Photothermal Deflection (PTD) studies on As20Te80-xGax (7.5 ≤ x ≤ 18.5) glasses, undertaken to elucidate the network topological thresholds, are described in chapter four. It has been found that all the As20Te80-xGax glasses studied exhibit memory type electrical switching. The switching voltage (VT) of these glasses increases monotonically with x, in the composition range 7.5 ≤ x ≤ 15.0. The increase in VT with gallium addition leads to a local maximum at x = 15.0 and VT decreases with x thereafter, reaching a distinct minimum at x = 17.5. Based on the variation with composition of the electrical switching voltages, the composition x = 15.0 and x = 17.5 have been identified to be the rigidity percolation and chemical thresholds of the As20Te80-xGax glassy system respectively. Further, the DSC studies indicate that As20Te80-xGax glasses exhibit a single glass transition (Tg) and two crystallization reactions (Tc1 & Tc2) upon heating. There is no appreciable change in Tg of As20Te80-xGax glasses with the addition of upto about10 atom% of Ga, whereas a continuous increase is seen in the crystallization temperature (Tc1). It is interesting to note that both Tg and Tc1 exhibit a maximum at x = 15.0 and a minimum at x = 17.5, the compositions identified to be the RPT and CT respectively by the switching experiments. The composition dependence of thermal diffusivity estimated from the PTD signal, indicate the occurrence of an extended stiffness transition in As20Te80-xGax glasses, with the compositions x = 9.0 and x = 15.0 being the onset and the completion of an extended rigidity percolation. A maximum and a minimum are seen in the thermal diffusivity respectively at these compositions. Further, a second maximum is seen in the thermal diffusivity of As20Te80-xGax glasses, the Chemical Threshold (CT) of the glassy system. The fifth chapter of the thesis describes the ADSC, electrical switching and photocurrent measurements on Ge15Te85-xInx (1 ≤ x ≤ 11) glasses. It is found there is not much change in the Tg of Ge15Te85-xInx glasses in the composition range 1 ≤ x ≤ 3. An increase is seen in Tg beyond x = 3, which continues until x = 11. Further, the composition dependence of non-reversing enthalpy shows the presence of a thermally reversing window in the compositions range x = 3 and x = 7. Electrical switching studies indicate that Ge15Te85-xInx glasses exhibit threshold type of switching at input currents below 2 mA. It is observed that switching voltages decrease initially with indium addition, exhibiting a minimum at x = 3, the onset of the extended rigidity percolation as revealed by ADSC. An increase is seen in VT above x = 3, which proceeds till x = 8, with a change in slope (lower to higher) seen around 7 atom% of indium which corresponds to the completion of the stiffness transition. The reversal in trend exhibited in the variation of VT at x = 8, leads to a well defined minimum around x = 9, the chemical threshold of the Ge15Te85-xInx glassy system. Photocurrent measurements indicate that there is no photodegradation in Ge15Te85-xInx glasses with x < 3, whereas samples with x ≥ 3 show photodegradation behavior. The composition dependent variation in the glass transition temperature has been attributed for this behavior. Further, the composition dependence of photo sensitivity has been found to show the signatures of the extended rigidity percolation and the chemical threshold in Ge15Te85-xInx glasses. The last chapter of thesis (chapter six) summarizes the results obtained and also the scope of future work to be undertaken.

Neste trabalho, a técnica de Lente Térmica (LT) foi usada para determinar o valor absoluto da difusividade térmica (D), da condutividade térmica (K) e do coeficiente de temperatura do caminho óptico (ds/tD) de vidros fluoretos dopados com cobalto e neodímio, calcogenetos, calcohaletos (mistura de calcogenetos com haletos), aluminate de cálcio e de um cristal fluoreto. Estas medidas foram efetuadas na temperatura ambiente e próxima de Tg para algumas amostras. Para o vidro ZBLAN, realizamos experimentos de LT da temperatura ambiente até ~ 330°C, observando um grande decréscimo de D na região de transição do vidro (Tg ~ 290°C). Nós também aplicamos a técnica de LT para determinar a eficiência quântica fluorescente do ZBLAN dopado com Nd+3. A utilidade desta técnica para determinar as propriedades termo-ópticas dos materiais transparentes em função da temperatura foi demonstrado. / In this work the Thermal Lens (TL) technique was used to determine the absolute values of the thermal diffusivity (D), thermal conductivity (K) and temperature coefficient of the optical path length (ds/dT) of fluoride, chalcogenide, chalcohalide (chalcogenides and halides mixture) and calcium aluminate glass and of a fluoride cristal. These measurements were developed at ambient temperature and near Tg for some samples. For the ZBLAN glass, we performed the TL experiment from ambient to ~ 330°C, observing na abrupt decrease on D close to the glass transition temperature (Tg ~ 290°C). We also applied the TL technique to determine the fluorescence quantum efficiency of Nd+3 doped ZBLAN. The usefulness of this technique to determine thermo-optical properties of transparent materials as a function of the temperature was demonstrated.

Este trabalho vem a dar uma importante contribuição à pesquisa de novos materiais que possam ser utilizados como meios ativos para lasers de estado sólido na região do infravermelho próximo, bombeados por lasers de diodo, e também na região do visível, bombeados pelo processo de Upconversion. As emissões dos íons Nd3+ e Tm3+ foram estudadas em três sistemas (cristalino, vítreo e policristalino). No primeiro sistema inclui-se fibras monocristalinas com diâmetro de 500 &#181;m e até 3 cm de comprimento dos vanadatos YVO4, Y0,8La0,2VO4 e Gd0,8La0,2VO4, dopadas com Nd3+, e de Gd0,8La0,2VO4 dopadas com Tm3+, que foram crescidas pela versátil técnica LHPG, de baixo custo, e caracterizadas dos pontos de vista estrutural e espectroscópico como candidatas para o desenvolvimento de lasers compactos na região do IV e do VIS. Foi observada emissão laser em 1,064&#181;, foi observada em uma fibra de YVO4:Nd3+ adaptada a uma cavidade end-pump, com eficiência comparável a de um cristal comercial crescido pelo método de Czochralski. Para os vidros calcogenetos GaLaS dopados com Nd3+ e Tm3+, além das caracterizações espectroscópicas, realizou-se o estudo da transferência de energia entre íons, das interações íon-matriz e da geração de calor nas amostras, para investigar a influência destes mecânicas na eficiência quântica de emissão dos íons. Para o GaLaS:Tm3+, verificou-se ganho óptico positivo em 1,8 &#181;m (emissão de interesse em medicina e odontologia), e medidas de absorção de estado excitado indicam que a transição em 1,4 &#181;m pode ser utilizada em amplificadores de banda larga, desde que seja bombeada apropriadamente. As amostras da cerâmica ferroelétrica PLZT(9/65/35) transparentes e dopadas com ambos os íons foram caracterizadas de maneira similar aos outros sistemas e cálculo das propriedades radiativas aliadas as medidas do espectro de ganho no PLZT:Nd3+ indicam a potencialidade dessas matrizes como meio ativo para lasers. / In this work we have made an important contribution to the growing research of new laser materials that can be pumped by low cost diode lasers or by the Upconversion process to operate in the near-infrared and visible spectral regions. Three kinds of hosts, doped with the rare earth ions (Nd3+ and Tm3+) were studied, and they present potential characteristics as laser active media. Single crystal fibers of yttrium and gadolinium orthovanadates grown by LHPG are very attractive for the construction of compact lasers due to the versatility and low cost of the growing process. A neodymium-doped YVO4 fiber adapted to an end-pump laser cavity presented efficient emission at 1.064 &#181;m, similar to that obtained for a Czochralski grown bulk crystal. A study of ion-ion and host-ion interactions was done for GaLaS glass to investigate the influence of these processes on fluorescence quantum efficiencies. For GaLaS:Tm3+, positive gain was estimated at 1,8 &#181;m and it was also observed that the 1,47 &#181;m emission is efficient under appropriate pumping. Finally, transparent PLZT ferroelectric ceramic samples were characterized and the results also point out that PLZT:Nd3+ might become a potential laser host.

Este trabalho vem a dar uma importante contribuição à pesquisa de novos materiais que possam ser utilizados como meios ativos para lasers de estado sólido na região do infravermelho próximo, bombeados por lasers de diodo, e também na região do visível, bombeados pelo processo de Upconversion. As emissões dos íons Nd3+ e Tm3+ foram estudadas em três sistemas (cristalino, vítreo e policristalino). No primeiro sistema inclui-se fibras monocristalinas com diâmetro de 500 &#181;m e até 3 cm de comprimento dos vanadatos YVO4, Y0,8La0,2VO4 e Gd0,8La0,2VO4, dopadas com Nd3+, e de Gd0,8La0,2VO4 dopadas com Tm3+, que foram crescidas pela versátil técnica LHPG, de baixo custo, e caracterizadas dos pontos de vista estrutural e espectroscópico como candidatas para o desenvolvimento de lasers compactos na região do IV e do VIS. Foi observada emissão laser em 1,064&#181;, foi observada em uma fibra de YVO4:Nd3+ adaptada a uma cavidade end-pump, com eficiência comparável a de um cristal comercial crescido pelo método de Czochralski. Para os vidros calcogenetos GaLaS dopados com Nd3+ e Tm3+, além das caracterizações espectroscópicas, realizou-se o estudo da transferência de energia entre íons, das interações íon-matriz e da geração de calor nas amostras, para investigar a influência destes mecânicas na eficiência quântica de emissão dos íons. Para o GaLaS:Tm3+, verificou-se ganho óptico positivo em 1,8 &#181;m (emissão de interesse em medicina e odontologia), e medidas de absorção de estado excitado indicam que a transição em 1,4 &#181;m pode ser utilizada em amplificadores de banda larga, desde que seja bombeada apropriadamente. As amostras da cerâmica ferroelétrica PLZT(9/65/35) transparentes e dopadas com ambos os íons foram caracterizadas de maneira similar aos outros sistemas e cálculo das propriedades radiativas aliadas as medidas do espectro de ganho no PLZT:Nd3+ indicam a potencialidade dessas matrizes como meio ativo para lasers. / In this work we have made an important contribution to the growing research of new laser materials that can be pumped by low cost diode lasers or by the Upconversion process to operate in the near-infrared and visible spectral regions. Three kinds of hosts, doped with the rare earth ions (Nd3+ and Tm3+) were studied, and they present potential characteristics as laser active media. Single crystal fibers of yttrium and gadolinium orthovanadates grown by LHPG are very attractive for the construction of compact lasers due to the versatility and low cost of the growing process. A neodymium-doped YVO4 fiber adapted to an end-pump laser cavity presented efficient emission at 1.064 &#181;m, similar to that obtained for a Czochralski grown bulk crystal. A study of ion-ion and host-ion interactions was done for GaLaS glass to investigate the influence of these processes on fluorescence quantum efficiencies. For GaLaS:Tm3+, positive gain was estimated at 1,8 &#181;m and it was also observed that the 1,47 &#181;m emission is efficient under appropriate pumping. Finally, transparent PLZT ferroelectric ceramic samples were characterized and the results also point out that PLZT:Nd3+ might become a potential laser host.

Neste trabalho, a técnica de Lente Térmica (LT) foi usada para determinar o valor absoluto da difusividade térmica (D), da condutividade térmica (K) e do coeficiente de temperatura do caminho óptico (ds/tD) de vidros fluoretos dopados com cobalto e neodímio, calcogenetos, calcohaletos (mistura de calcogenetos com haletos), aluminate de cálcio e de um cristal fluoreto. Estas medidas foram efetuadas na temperatura ambiente e próxima de Tg para algumas amostras. Para o vidro ZBLAN, realizamos experimentos de LT da temperatura ambiente até ~ 330°C, observando um grande decréscimo de D na região de transição do vidro (Tg ~ 290°C). Nós também aplicamos a técnica de LT para determinar a eficiência quântica fluorescente do ZBLAN dopado com Nd+3. A utilidade desta técnica para determinar as propriedades termo-ópticas dos materiais transparentes em função da temperatura foi demonstrado. / In this work the Thermal Lens (TL) technique was used to determine the absolute values of the thermal diffusivity (D), thermal conductivity (K) and temperature coefficient of the optical path length (ds/dT) of fluoride, chalcogenide, chalcohalide (chalcogenides and halides mixture) and calcium aluminate glass and of a fluoride cristal. These measurements were developed at ambient temperature and near Tg for some samples. For the ZBLAN glass, we performed the TL experiment from ambient to ~ 330°C, observing na abrupt decrease on D close to the glass transition temperature (Tg ~ 290°C). We also applied the TL technique to determine the fluorescence quantum efficiency of Nd+3 doped ZBLAN. The usefulness of this technique to determine thermo-optical properties of transparent materials as a function of the temperature was demonstrated.