Photodétecteurs infrarouge par absorption à deux photons

The core issue of current photosensors is related to their operating temperature. This manuscript introduces a new detection field with two-photon absorption detectors. The goal is to achieve infrared detection at room temperature. Dark noise is reduced by using high gap energy materials rather than cryogenics. This evolution leads to new detection problems because of low two-photon absorption efficiency. It is indeed too weak to generate a detectable photocurrent. Moreover, there is a competition between others absorption mechanisms involving energies below the gap. That’s why we suggest using nanostructures. These are sub-wavelength structures capable of confining and focusing light in a material. Thus the light intensity is exalted over several orders of magnitude. Therefore nanostructures lead to a photocurrent gain.The objective of this thesis is to evaluate this new detection field’s potential for infrared. The work is then discussed into four sections. Several themes are crossed, such as infrared detection, nonlinear optics and nanostructures. So a first chapter of general introduction gathers the whole. Two-photon absorption issues are introduced, leading to the use of nanostructures.I develop in the second chapter a methodology of optimisation for a nanostructured two-photon absorption photodetector. This tunable method is finally used on several detection configurations.A third chapter displays the photodiode characterisations. Along with the bench specifications, experimental issues are considered. The first sample results brought lots of information, inspiring the creation and characterisation of a last generation.A transition towards quantum wells is finally discussed in a last section. Using quantum wells over bulk semiconductors leads indeed to an increase of additional orders of magnitude of the non-degenerated two-photon absorption coefficient. Since this enhancement is only due to the material, it is compatible with nanostructures. Therefore it has motivated the writing of this theoretical chapter dealing with these transitions stakes.Au coeur des problématiques liées à la température de fonctionnement des détecteurs infrarouge, ce manuscrit introduit une nouvelle jeune filière technologique : les photodétecteurs employant l’absorption à deux photons. L’objectif est de proposer une rupture visant à réaliser de la détection infrarouge à température ambiante. L’enjeu est de réduire le bruit d’obscurité par l’utilisation de matériaux à grande énergie de gap plutôt que par cryogénie. Cette évolution introduit de nouvelles problématiques, car l’efficacité du mécanisme d’absorption à deux photons est trop faible pour générer seule un photocourant détectable. De plus, elle présente le risque d’être concurrencée par d’autres mécanismes d’absorption d’énergie inférieure au gap. C’est pourquoi nous proposons l’utilisation de nanostructures afin d’y remédier : il s’agit de structures sub-longueur d’onde, capables de confiner et concentrer la lumière dans un matériau. Ainsi, l’intensité lumineuse est exaltée sur plusieurs ordres de grandeurs, introduisant par conséquent un gain sur le photocourant généré.L’objectif de cette thèse est d’établir le potentiel de cette jeune filière pour la détection infrarouge, discussion divisée en quatre sections. Au croisement de plusieurs thématiques telles que la détection infrarouge, l’optique non linéaire, et les nanostructures, un premier chapitre d’introduction générale permet d’en concilier l’ensemble. Les problématiques liées à l’absorption à deux photons y sont présentées, amenant finalement à employer les nanostructures comme solution.Je propose une méthodologie de conception au cours du second chapitre qui permet d’optimiser une structure pour l’absorption à deux photons. Versatile et accordable, elle est ensuite mise en oeuvre sur plusieurs configurations de détection.Le troisième chapitre présente les caractérisations des photodiodes réalisées. J’y détaille les difficultés expérimentales rencontrées au cours des mesures, nécessitant l’emploi d’un banc spécifique. Les résultats obtenus sur les échantillons ont amené beaucoup de discussions, inspirant la création d’une dernière génération.Dans une dernière section, je discute d’une perspective de transition des photodiodes vers des puits quantiques. En effet, il a récemment été montré que le coefficient d’absorption à deux photons non-dégénéré gagne un voire deux ordres de grandeurs en comparaison du semiconducteur massif. Ce gain uniquement lié au matériau, et compatible avec les nanostructures, a motivé l’écriture d’un chapitre théorique discutant des enjeux d’une telle transition

Two-photon absorption for infrared photodetectors

Au coeur des problématiques liées à la température de fonctionnement des détecteurs infrarouge, ce manuscrit introduit une nouvelle jeune filière technologique : les photodétecteurs employant l’absorption à deux photons. L’objectif est de proposer une rupture visant à réaliser de la détection infrarouge à température ambiante. L’enjeu est de réduire le bruit d’obscurité par l’utilisation de matériaux à grande énergie de gap plutôt que par cryogénie. Cette évolution introduit de nouvelles problématiques, car l’efficacité du mécanisme d’absorption à deux photons est trop faible pour générer seule un photocourant détectable. De plus, elle présente le risque d’être concurrencée par d’autres mécanismes d’absorption d’énergie inférieure au gap. C’est pourquoi nous proposons l’utilisation de nanostructures afin d’y remédier : il s’agit de structures sub-longueur d’onde, capables de confiner et concentrer la lumière dans un matériau. Ainsi, l’intensité lumineuse est exaltée sur plusieurs ordres de grandeurs, introduisant par conséquent un gain sur le photocourant généré.L’objectif de cette thèse est d’établir le potentiel de cette jeune filière pour la détection infrarouge, discussion divisée en quatre sections. Au croisement de plusieurs thématiques telles que la détection infrarouge, l’optique non linéaire, et les nanostructures, un premier chapitre d’introduction générale permet d’en concilier l’ensemble. Les problématiques liées à l’absorption à deux photons y sont présentées, amenant finalement à employer les nanostructures comme solution.Je propose une méthodologie de conception au cours du second chapitre qui permet d’optimiser une structure pour l’absorption à deux photons. Versatile et accordable, elle est ensuite mise en oeuvre sur plusieurs configurations de détection.Le troisième chapitre présente les caractérisations des photodiodes réalisées. J’y détaille les difficultés expérimentales rencontrées au cours des mesures, nécessitant l’emploi d’un banc spécifique. Les résultats obtenus sur les échantillons ont amené beaucoup de discussions, inspirant la création d’une dernière génération.Dans une dernière section, je discute d’une perspective de transition des photodiodes vers des puits quantiques. En effet, il a récemment été montré que le coefficient d’absorption à deux photons non-dégénéré gagne un voire deux ordres de grandeurs en comparaison du semiconducteur massif. Ce gain uniquement lié au matériau, et compatible avec les nanostructures, a motivé l’écriture d’un chapitre théorique discutant des enjeux d’une telle transition.The core issue of current photosensors is related to their operating temperature. This manuscript introduces a new detection field with two-photon absorption detectors. The goal is to achieve infrared detection at room temperature. Dark noise is reduced by using high gap energy materials rather than cryogenics. This evolution leads to new detection problems because of low two-photon absorption efficiency. It is indeed too weak to generate a detectable photocurrent. Moreover, there is a competition between others absorption mechanisms involving energies below the gap. That’s why we suggest using nanostructures. These are sub-wavelength structures capable of confining and focusing light in a material. Thus the light intensity is exalted over several orders of magnitude. Therefore nanostructures lead to a photocurrent gain.The objective of this thesis is to evaluate this new detection field’s potential for infrared. The work is then discussed into four sections. Several themes are crossed, such as infrared detection, nonlinear optics and nanostructures. So a first chapter of general introduction gathers the whole. Two-photon absorption issues are introduced, leading to the use of nanostructures.I develop in the second chapter a methodology of optimisation for a nanostructured two-photon absorption photodetector. This tunable method is finally used on several detection configurations.A third chapter displays the photodiode characterisations. Along with the bench specifications, experimental issues are considered. The first sample results brought lots of information, inspiring the creation and characterisation of a last generation.A transition towards quantum wells is finally discussed in a last section. Using quantum wells over bulk semiconductors leads indeed to an increase of additional orders of magnitude of the non-degenerated two-photon absorption coefficient. Since this enhancement is only due to the material, it is compatible with nanostructures. Therefore it has motivated the writing of this theoretical chapter dealing with these transitions stakes

Methodology of optimisation for a nanostructured two-photon absorption photodetector

We introduce a 3-step method to optimise a nanostructured photodetector for infrared sensing through non degenerated two-photon absorption (NDTPA). First, the nanostructure is designed to tailor the distribution and concentration of both pump and signal intensities within the absorbing layer, thus leading to a gain in two-photon absorption. Second, the issue of the competition between NDTPA and other sub-bandgap transitions is tackled with a new figure of merit to favor as much as possible NDTPA while minimising other absorption processes. Third, a refined computation of the gain and the figure of merit is done to consider focused beams. Finally, two scenarios based on low power infrared photodetection are investigated to illustrate the flexibility and adaptibility of the method. It is shown that the gain is up to 7 times higher and the figure of merit is up to 20 times higher compared to the literature

Optimized bi-resonant nanostructured diode for infrared photodetection through non degenerate two-photon absorption

International audienceTwo-photon absorption (TPA) is a third order non-linear process that relies on the quasi-simultaneous absorption of two photons. Therefore, it has been proved to be an interesting tool to measure ultra-fast correlations 1 or to design all-optical switches. 2 Yet, due to the intrinsically low efficiency of the non-linear processes, these applications rest upon high peak power light sources such as femtosecond and picosecond pulsed laser. However TPA has also been noticed as an appealing new scheme for quantum infrared detection. 3, 4 Indeed, typical quantum detection of IR radiation is based on small gap semiconductors that need to be cooled down to cryogenic temperature to achieve sufficient detectivity. TPA enables the absorption of IR photons by wide gap semiconductors when pump photons are provided to complete optical transitions across the gap. Still, the low efficiency of TPA represents a difficulty to detect usual infrared photon fluxes. To tackle this issue, we combined three strategies to improve the detection efficiency. First, it has been proved theoretically and experimentally that using different pump and signal photon energies, which is known as non degenerate TPA (NDTPA), help increasing the TPA efficiency by several orders of magnitude. 5 Secondly, it is well known that TPA has a quadratic dependence with the signal electric fields modulus, so we designed a specific nanostructure to enhance the signal field inside the active medium of the detector. Finally, since TPA is a local quasi-instantaneous process, both pump and signal photons must be temporarily and spatially co-localized inside the active medium. We made sure to maximize the overlap of the fields inside our device. In this proceeding, we report the concepts of nanostructures and how it influences TPA absorption in a PIN photodiode. Experimental data point out that infrared photons were detected inside our first generation of diodes. However some issues are still to deal with to reach infrared detection with low fluxes thermal sources. The SNR (signal to noise ratio) can be widely improved by reaching higher values of NDTPA photocurrent and limiting the sub-gap absorptions mainly responsible for the structure noise. Consequently a second generation of nanostructured photodiodes has been designed to perform better detection. NDTPA theory The expected photocurrent generation in a PIN junction through two-photon absorption is a sum of three terms: (1) the linear absorption current, (2) the degenerate TPA current of the pump and (3) the NDTPA-generated photocurrent : J total = α (ω p) I p + β (ω p , ω p) I 2 p + β (ω p , ω s) I p I s (1) Where I p (resp. I s) is the intensity [W/m 2 ] of the pump (resp. signal) beam, · represent the integration in the i-layer, the α is the linear absorption coefficient and β is the TPA coefficient. The first term comes from a linear absorption of sub-bandgap photons from the pump light. This phenomenon has been studied in several materials (silicium, gallium arsenide) and is explained as a photo-assisted Shockley-Read-Hall (PASRH) process. 6, 7 The second term is the degenerate two-photon absorption of the pump. 3 The last one comes from the non-degenerat

Changes in the Intermediate Water Masses of the Mediterranean Sea During the Last Climatic Cycle—New Constraints From Neodymium Isotopes in Foraminifera

International audienceThe Mediterranean Sea is a semi-enclosed basin characterized by arid conditions and connected to the North Atlantic through the Strait of Gibraltar (sill depth of ∼300 m). This generates a Mediterranean thermohaline circulation where the inflow of relatively fresh and cold surface Atlantic water (AW) is transformed into intermediate and deep waters in the Gulf of Lions, the Adriatic Sea, the Levantine Basin and the Aegean Sea (Robinson et al., 2001; Schroeder et al., 2012). In particular, the Levantine Intermediate Water (LIW) is formed in the Cyprus-Rhodes area from where it spreads westwards into the entire Mediterranean Sea at water depths of between ∼150 and 700 m (Lascaratos et al., 1993; Malanotte-Rizzoli et al., 1999). This overturning circulation is associated with an outflow of saltier and warmer intermediate water into the North Atlantic corresponding to the Mediterranean Outflow Water (MOW) (Robinson et al., 2001; Schroeder et al., 2012). Because the MOW contains up to ∼80% of LIW, the water mass formation in the Levantine Sea plays an important role for the salty outflow to the North Atlantic through the Strait of Gibraltar. A link between the intensification of the MOW and the intensity of the Atlantic Meridional Overturning Circulation (AMOC) has been proposed

A comprehensive experimental and kinetic modeling study of di-isobutylene isomers : Part 1

Di-isobutylene has received significant attention as a promising fuel blendstock, as it can be synthesized via biological routes and is a short-listed molecule from the Co-Optima initiative. Di-isobutylene is also popularly used as an alkene representative in multi-component surrogate models for engine studies of gasoline fuels. However, there is limited experimental data available in the literature for neat di-isobutylene under engine-like conditions. Hence, most existing di-isobutylene models have not been extensively validated, particularly at lower temperatures (< 1000 K). Most gasoline surrogate models include the di-isobutylene sub-mechanism published by Metcalfe et al. [1] with little or no modification. The current study is undertaken to develop a detailed kinetic model for di-isobutylene and validate the model using a wide range of relevant experimental data. Part 1 of this study exclusively focuses on the low- to intermediate temperature kinetics of di-isobutylene. An upcoming part 2 discusses the high-temperature model development and validation of the relevant experimental targets. Ignition delay time measurements for the di-isobutylene isomers were performed at pressures ranging from 15 – 30 bar at equivalence ratios of 0.5, 1.0, and 2.0 diluted in air and in the temperature range 650 – 900 K using two independent rapid compression machine facilities. In addition, measurements of species identified during the oxidation of these isomers were performed in a jet-stirred reactor and in a rapid compression machine. A detailed kinetic model for the di-isobutylene isomers is developed to capture the wide range of new experimental targets. For the first time, a comprehensive low-temperature chemistry submodel is included. The differences in the important reaction pathways for the accurate prediction of the oxidation of the two DIB isomers are compared using reaction path analysis. The most sensitive reactions controlling the ignition delay times of the DIB isomers under the pressure and temperature conditions necessary for autoignition in engines are identified

Temporal Trends in Transcatheter Aortic Valve Replacement in France: FRANCE 2 to FRANCE TAVI

International audienceBackground - Transcatheter aortic valve replacement (TAVR) is standard therapy for patients with severe aortic stenosis who are at high surgical risk. However, national data regarding procedural characteristics and clinical outcomes over time are limited. Objectives - The aim of this study was to assess nationwide performance trends and clinical outcomes of TAVR during a 6-year period. Methods - TAVRs performed in 48 centers across France between January 2013 and December 2015 were prospectively included in the FRANCE TAVI (French Transcatheter Aortic Valve Implantation) registry. Findings were further compared with those reported from the FRANCE 2 (French Aortic National CoreValve and Edwards 2) registry, which captured all TAVRs performed from January 2010 to January 2012 across 34 centers. Results - A total of 12,804 patients from FRANCE TAVI and 4,165 patients from FRANCE 2 were included in this analysis. The median age of patients was 84.6 years, and 49.7% were men. FRANCE TAVI participants were older but at lower surgical risk (median logistic European System for Cardiac Operative Risk Evaluation [EuroSCORE]: 15.0% vs. 18.4%; p < 0.001). More than 80% of patients in FRANCE TAVI underwent transfemoral TAVR. Transesophageal echocardiography guidance decreased from 60.7% to 32.3% of cases, whereas more recent procedures were increasingly performed in hybrid operating rooms (15.8% vs. 35.7%). Rates of Valve Academic Research Consortium-defined device success increased from 95.3% in FRANCE 2 to 96.8% in FRANCE TAVI (p < 0.001). In-hospital and 30-day mortality rates were 4.4% and 5.4%, respectively, in FRANCE TAVI compared with 8.2% and 10.1%, respectively, in FRANCE 2 (p < 0.001 for both). Stroke and potentially life-threatening complications, such as annulus rupture or aortic dissection, remained stable over time, whereas rates of cardiac tamponade and pacemaker implantation significantly increased. Conclusions - The FRANCE TAVI registry provided reassuring data regarding trends in TAVR performance in an all-comers population on a national scale. Nonetheless, given that TAVR indications are likely to expand to patients at lower surgical risk, concerns remain regarding potentially life-threatening complications and pacemaker implantation. (Registry of Aortic Valve Bioprostheses Established by Catheter [FRANCE TAVI]; NCT01777828)