Performance evaluation of a quantum-well infrared photodetector in patch-antenna architecture

Nel presente lavoro di tesi si dimostra il miglioramento delle perfomances di un detector basato su pozzi quantici (QWIP-Quantum Well Infrared Photo detector)(n-type GaAs/AlGaAs) nel range infrarosso (λ ≈8.6µm), processato in un array di nano-antenne a doppio metallo. I Quantum Well detectors generano fotocorrente attivando transizioni intersottobanda nel supereticolo di pozzi quantici. Le prestazioni di questi detectors sono deteriorate dal rumore associato alla corrente di dark, proporzionale all’area del detector e dipendente esponenzialemente dalla temperatura. In questo lavoro, si dimostra che le antenne patches agiscono da micro-cavitá che confinano il campo elettrico incidente in uno strato di semiconduttore con dimensioni minori della lunghezza d’onda, evitano la regola di selezione intersottobanda e raccolgono fotoni da un’area maggiore delle dimensioni fisiche del dispositivo stesso, riducendo la corrente di dark senza diminuire la fotocorrente. Il miglioramento delle prestazioni del detector é espresso in termini di area di collezione Acoll e di focusing factor, l’aumento di campo locale. Queste quantitá sono state estratte da spettri di riflettivitá presi tramite spettroscopia infrarosso a Trasformata di Fourier (FTIR) a 300K. Caratteristiche tensione-corrente sono state misurate in condizioni dark e di background (300K) da 4K a 300K, e paragonate ad un dispositivo con la stessa regione attiva ma processato con una faccetta a 45 °. Da queste curve la temperatura di BLIP (Background Infrared Limited Performance) è stata ricavata. Misure di fotocorrente in funzione del bias sono state prese tramite tecnica con amplificatore lock-in. Le figure di merito responsivitá e detectivity sono state estratte dalle misure di fotocorrente, dopo la calibrazione della potenza radiativa incidente. Queste misure mostrano un miglioramento di 10K nelle performaneces rispetto al dispositivo mesa, dimostrando un’elevata sensibilitá fino a temperatura ambiente

Towards a Better Understanding of OPD Limitations for Higher Sensitivity and Contrast at the VLTI

Precise control of the optical path differences (OPD) in the Very Large Telescope Interferometer (VLTI) was critical for the characterization of the black hole at the center of our Galaxy - leading to the 2020 Nobel prize in physics. There is now significant effort to push these OPD limits even further, in-particular achieving 100nm OPD RMS on the 8m unit telescopes (UT's) to allow higher contrast and sensitivity at the VLTI. This work calculated the theoretical atmospheric OPD limit of the VLTI as 5nm and 15nm RMS, with current levels around 200nm and 100nm RMS for the UT and 1.8m auxillary telescopes (AT's) respectively, when using bright targets in good atmospheric conditions. We find experimental evidence for the $f^{-17/3}$ power law theoretically predicted from the effect of telescope filtering in the case of the ATs which is not currently observed for the UT's. Fitting a series of vibrating mirrors modelled as dampened harmonic oscillators, we were able to model the UT OPD PSD of the gravity fringe tracker to $<1nm/\sqrt{Hz}$ RMSE up to 100Hz, which could adequately explain a hidden $f^{-17/3}$ power law on the UTs. Vibration frequencies in the range of 60-90Hz and also 40-50Hz were found to generally dominate the closed loop OPD residuals of Gravity. Cross correlating accelerometer with Gravity data, it was found that strong contributions in the 40-50Hz range are coming from the M1-M3 mirrors, while a significant portion of power from the 60-100Hz contributions are likely coming from between the M4-M10. From the vibrating mirror model it was shown that achieving sub 100nm OPD RMS for particular baselines (that have OPD$\sim$200nm RMS) required removing nearly all vibration sources below 100Hz

Asgard/NOTT: L-band nulling interferometry at the VLTI I. Simulating the expected high-contrast performance

Context: NOTT (formerly Hi-5) is a new high-contrast L' band (3.5-4.0 \textmu m) beam combiner for the VLTI with the ambitious goal to be sensitive to young giant exoplanets down to 5 mas separation around nearby stars. The performance of nulling interferometers in these wavelengths is affected both by fundamental noise from the background and by the contributions of instrumental noises. This motivates the development of end-to-end simulations to optimize these instruments. Aims: To enable the performance evaluation and inform the design of such instruments on the current and future infrastructures, taking into account the different sources of noise, and their correlation. Methods: SCIFYsim is an end-to-end simulator for single mode filtered beam combiners, with an emphasis on nulling interferometers. It is used to compute a covariance matrix of the errors. Statistical detection tests based on likelihood ratios are then used to compute compound detection limits for the instrument. Results: With the current assumptions on the performance of the wavefront correction systems, the errors are dominated by correlated instrumental errors down to stars of magnitude 6-7 in the L band, beyond which thermal background from the telescopes and relay system becomes dominant. Conclusions: SCIFYsim is suited to anticipate some of the challenges of design, tuning, operation and signal processing for integrated optics beam combiners. The detection limits found for this early version of NOTT simulation with the unit telescopes are compatible with detections at contrasts up to $10^5$ in the L band at separations of 5 to 80 mas around bright stars

Technical requirements and optical design of the Hi-5 spectrometer

Hi-5 is a proposed L’ band high-contrast nulling interferometric instrument for the visitor focus of the Very Large Telescope Interferometer (VLTI). As a part of the ERC consolidator project called SCIFY (Self-Calibrated Interferometry For exoplanet spectroscopY), the instrument aims to achieve sufficient dynamic range and angular resolution to directly image and characterize the snow line of young extra-solar planetary systems. The spectrometer is based on a dispersive grism and is located downstream of an integrated optics beam- combiner. To reach the contrast and sensitivity specifications, the outputs of the I/O chip must be sufficiently separated and properly sampled on the Hawaii-2RG detector. This has many implications for the photonic chip and spectrometer design. We present these technical requirements, trade-off studies, and phase-A of the optical design of the Hi-5 spectrometer in this paper. For both science and contract-driven reasons, the instrument design currently features three different spectroscopic modes (R=20, 400, and 2000). Designs and efficiency estimates for the grisms are also presented as well as the strategy to separate the two polarization states.SCIF

The GRAVITY+ Project: Towards All-sky, Faint-Science, High-Contrast Near-Infrared Interferometry at the VLTI

The GRAVITY instrument has been revolutionary for near-infrared interferometry by pushing sensitivity and precision to previously unknown limits. With the upgrade of GRAVITY and the Very Large Telescope Interferometer (VLTI) in GRAVITY+, these limits will be pushed even further, with vastly improved sky coverage, as well as faint-science and high-contrast capabilities. This upgrade includes the implementation of wide-field off-axis fringe-tracking, new adaptive optics systems on all Unit Telescopes, and laser guide stars in an upgraded facility. GRAVITY+ will open up the sky to the measurement of black hole masses across cosmic time in hundreds of active galactic nuclei, use the faint stars in the Galactic centre to probe General Relativity, and enable the characterisation of dozens of young exoplanets to study their formation, bearing the promise of another scientific revolution to come at the VLTI.Comment: Published in the ESO Messenge

Récepteurs unipolaires non-refroidis pour la détection hétérodyne dans la deuxième fenêtre de transparence atmosphérique

Mon travail de thèse de doctorat porte sur la conception et la réalisation d’un système de détection sensible à 9 μm de longueur d’onde, dans lequel tous les composants sont des dispositifs semi-conducteurs non refroidis. Cet objectif est atteint en exploitant deux avancées majeures : un détecteur amélioré par métamatériau et un schéma hétérodyne avec des lasers à cascade quantique. Les détecteurs étudiés sont des détecteurs à cascade quantique (QCD) et à puits quantiques (QWIP), dispositifs unipolaires où la transition optique a lieu entre des états électroniques confinés dans la bande de conduction. Ils sont intéressants pour la détection hétérodyne car leur temps de relaxation est extrêmement court et, par conséquent, ils ont une réponse rapide et hautement linéaire même sous un éclairage intense. Dans ce travail, je décris la physique microscopique nécessaire pour comprendre la réponse du dispositif à l’excitation lumineuse, avec un aperçu des phénomènes liés au transport électronique quantique. Je rapporte l’évaluation des performances d’un QCD à 9 μm inséré dans un métamatériau de type antenne. L’antenne augmente le flux de photons incident sur le détecteur. Ceci permet de réduire l’aire électrique du détecteur et donc le courant d’obscurité, qui améliore très significativement les performances à haute température. La sensibilité et la bande passante du détecteur ont été testées dans un système hétérodyne entièrement optimisé utilisant une stabilisation passive des lasers et une conception précise de l’optique infrarouge. Enfin, je démontre que l’injection de signal hyperfréquence dans les récepteurs décale le battement hétérodyne sur toute la large bande passante des détecteurs.The work of my PhD thesis focuses on the conception and realization of a sensitive detection set-up at 9 μm wavelength, where all components are uncooled semiconductor devices. The project is realized by exploiting two major advances: a metamaterial-enhanced detector and a heterodyne scheme with quantum cascade lasers. The investigated detectors are quantum cascade (QCD) and quantum well detectors (QWIP), unipolar devices where the optical transition takes place between confined electronic states in the conduction band. They are attractive for heterodyne detection as their carrier lifetime is extremely short and therefore, they have a fast and highly linear response under strong illumination. In this work, I describe the microscopic physics necessary to understand the device response to light solicitation,with an insight on the phenomena related to quantum electronic transport. I reportthe performances evaluation of a 9 μm QCD processed into an antenna-based metamaterial. The antenna increases the photon flux that impinges on the detector. This allows a reduction of the detector electrical area and consequently of the dark current, enabling much better performances at high-temperature. The detector sensitivity and bandwidth has been tested with a heterodyne system fully optimized using passive stabilization of the lasers and an accurate conception of the infrared optics. Finally, I demonstrate that the injection of microwave signal into the receivers shifts the heterodyne beating over the large bandwidth of the devices

Récepteurs unipolaires non-refroidis pour la détection hétérodyne dans la deuxième fenêtre de transparence atmosphérique

The work of my PhD thesis focuses on the conception and realization of a sensitive detectionset-up at 9 µm wavelength, where all components are uncooled semiconductor devices. Theproject is realized by exploiting two major advances: a metamaterial-enhanced detector anda heterodyne scheme with quantum cascade lasers. The investigated detectors are quantumcascade (QCD) and quantum well detectors (QWIP), unipolar devices where the opticaltransition takes place between confined electronic states in the conduction band. They areattractive for heterodyne detection as their carrier lifetime is extremely short and therefore, they have a fast and highly linear response under strong illumination. In this work, Idescribe the microscopic physics necessary to understand the device response to light solicitation, with an insight on the phenomena related to quantum electronic transport. I reportthe performances evaluation of a 9 µm QCD processed into an antenna-based metamaterial. The antenna increases the photon flux that impinges on the detector. This allows areduction of the detector electrical area and consequently of the dark current, enabling muchbetter performances at high-temperature. The detector sensitivity and bandwidth has beentested with a heterodyne system fully optimized using passive stabilization of the lasers andan accurate conception of the infrared optics. Finally, I demonstrate that the injection ofmicrowave signal into the receivers shifts the heterodyne beating over the large bandwidthof the devices.Mon travail de thèse de doctorat porte sur la conception et la réalisation d’un système de détection sensible à 9 µm de longueur d’onde, dans lequel tous les composants sont des dispositifssemi-conducteurs non refroidis. Cet objectif est atteint en exploitant deux avancées majeures :un détecteur amélioré par métamatériau et un schéma hétérodyne avec des lasers à cascade quantique. Les détecteurs étudiés sont des détecteurs à cascade quantique (QCD) et à puits quantiques(QWIP), dispositifs unipolaires où la transition optique a lieu entre des états électroniques confinés dans la bande de conduction. Ils sont intéressants pour la détection hétérodyne car leurtemps de relaxation est extrêmement court et, par conséquent, ils ont une réponse rapide et hautement linéaire même sous un éclairage intense. Dans ce travail, je décris la physique microscopique nécessaire pour comprendre la réponse du dispositif à l’excitation lumineuse, avec un aperçu des phénomènes liés au transport électronique quantique. Je rapporte l’évaluation des performances d’un QCD à 9 µm inséré dans un métamatériau de type antenne. L’antenne augmente le flux dephotons incident sur le détecteur. Ceci permet de réduire l’aire électrique du détecteur et donc lecourant d’obscurité, qui améliore très significativement les performances à haute température. Lasensibilité et la bande passante du détecteur ont été testées dans un système hétérodyne entièrement optimisé utilisant une stabilisation passive des lasers et une conception précise de l’optiqueinfrarouge. Enfin, je démontre que l’injection de signal hyperfréquence dans les récepteurs décalele battement hétérodyne sur toute la large bande passante des détecteurs

Récepteurs unipolaires non-refroidis pour la détection hétérodyne dans la deuxième fenêtre de transparence atmosphérique

The work of my PhD thesis focuses on the conception and realization of a sensitive detection set-up at 9 μm wavelength, where all components are uncooled semiconductor devices. The project is realized by exploiting two major advances: a metamaterial-enhanced detector and a heterodyne scheme with quantum cascade lasers. The investigated detectors are quantum cascade (QCD) and quantum well detectors (QWIP), unipolar devices where the optical transition takes place between confined electronic states in the conduction band. They are attractive for heterodyne detection as their carrier lifetime is extremely short and therefore, they have a fast and highly linear response under strong illumination. In this work, I describe the microscopic physics necessary to understand the device response to light solicitation,with an insight on the phenomena related to quantum electronic transport. I reportthe performances evaluation of a 9 μm QCD processed into an antenna-based metamaterial. The antenna increases the photon flux that impinges on the detector. This allows a reduction of the detector electrical area and consequently of the dark current, enabling much better performances at high-temperature. The detector sensitivity and bandwidth has been tested with a heterodyne system fully optimized using passive stabilization of the lasers and an accurate conception of the infrared optics. Finally, I demonstrate that the injection of microwave signal into the receivers shifts the heterodyne beating over the large bandwidth of the devices.Mon travail de thèse de doctorat porte sur la conception et la réalisation d’un système de détection sensible à 9 μm de longueur d’onde, dans lequel tous les composants sont des dispositifs semi-conducteurs non refroidis. Cet objectif est atteint en exploitant deux avancées majeures : un détecteur amélioré par métamatériau et un schéma hétérodyne avec des lasers à cascade quantique. Les détecteurs étudiés sont des détecteurs à cascade quantique (QCD) et à puits quantiques (QWIP), dispositifs unipolaires où la transition optique a lieu entre des états électroniques confinés dans la bande de conduction. Ils sont intéressants pour la détection hétérodyne car leur temps de relaxation est extrêmement court et, par conséquent, ils ont une réponse rapide et hautement linéaire même sous un éclairage intense. Dans ce travail, je décris la physique microscopique nécessaire pour comprendre la réponse du dispositif à l’excitation lumineuse, avec un aperçu des phénomènes liés au transport électronique quantique. Je rapporte l’évaluation des performances d’un QCD à 9 μm inséré dans un métamatériau de type antenne. L’antenne augmente le flux de photons incident sur le détecteur. Ceci permet de réduire l’aire électrique du détecteur et donc le courant d’obscurité, qui améliore très significativement les performances à haute température. La sensibilité et la bande passante du détecteur ont été testées dans un système hétérodyne entièrement optimisé utilisant une stabilisation passive des lasers et une conception précise de l’optique infrarouge. Enfin, je démontre que l’injection de signal hyperfréquence dans les récepteurs décale le battement hétérodyne sur toute la large bande passante des détecteurs

Sviluppo di programma in LabVIEW per controllo di pressione in apparato Sievert

In questa tesi si propone un progetto software per il controllo automatico delle pressioni in apparato volumetrico, o apparato Sievert, dedicato allo studio dell'assorbimento e desorbimento di idrogeno nei metalli. Si introduce la fisica che regola la formazione degli idruri metallici, e i parametri di studio importanti per lo sviluppo di un sistema energetico basato sull'idrogeno. Particolare attenzione viene data alla misura di cinetica, la percentuale in peso di idrogeno assorbito/desorbito in funzione del tempo. Nel capitolo 2 si mostra il principio di funzionamento di un apparato Sievert e la realizzazione hardware dell'apparato: si compone di una serie di volumi calibrati, separati da valvole, a temperatura costante, tra cui la camera porta-campioni . La pressione al loro interno viene variata immettendo o aspirando idrogeno. Nel capitolo 3 è sviluppata la procedura di controllo software tramite LabVIEW, che si impone di impostare una pressione intermedia su un volume parziale, conoscendo la pressione finale, a volumi collegati, alla quale studiare il campione. Questo modo di lavoro permette di non agire direttamente sul campione con le immissioni e le aspirazioni di idrogeno. Il programma è stato provato con misure per materiali dalla cinetica molto veloce come il palladio(Pd). I risultati, nel capitolo 4, mostrano che il programma è in grado di controllare efficacemente le variazioni di pressioni e la misura di cinetica