No description available.

This thesis describes work on a novel 3D imaging system that successfully implements optical feedback and noise rejection mechanisms. The system is a combination of three relatively new technologies, namely, holographic projection, Time of Flight (ToF) ranging and Single Photon Avalanche Diode (SPAD) sensors. Holographic projection is used to provide structured illumination with optical feedback instead of more commonly used uniform illumination in similar imaging systems. It is obtained using a Ferro-electric Liquid Crystal on Silicon Spatial Light Modulator (FLCoS SLM). The structured illumination with optical feedback can be operated at up to 60 Hz with the current device, and has been shown to provide an average gain of about 1.56 in useful light levels. Alternatively, a gain over a limited area of up to a factor of 9 is possible with the current system. Time of Flight ranging is a method of choice for the system when depth estimation is concerned. It works even at very low light levels and allows for sub-centimetre depth resolution. ToF method was implemented using 20 MHz laser diode with 50 ps pulse duration and 200 mW peak power, as well as a SPAD sensor. The SPAD sensor consisted of a 32 32 array of 50 μm pixels, each with 10 bit Time to Digital Converter (TDC) with 50 ps timing resolution. Sensor pixels feature 100 Hz mean Dark Count Rate (DCR). The use of SPAD sensors with an adaptive sensing algorithm presented in this work has been demonstrated to reduce effective noise levels as seen by the sensor by a factor of 16. As a result, a significant gain in depth resolution can be achieved. The quantification of this gain is explained in more detail within this work. Furthermore, the work describes in detail system design, methodology of experimental procedure as well as different algorithms essential to the correct operation of the system. Significant amount of time is dedicated to diffraction pattern generation for the use in holographic projection, as well as modelling of photon detection in SPAD sensors and associated peak detection necessary to extract depth information from histograms of timed of photons. Moreover, the thesis discusses potential applications for the system based on the results of system characterisation presented in this work. The current state of the system suggests best suitability for gaming and machine vision applications. Finally, the work offers potential solutions to the practical issues that remain unresolved in the current system, alternatives for components used and paths for potential future development of the system proposed.

[pt] Apesar da alta sensibilidade alcançada por Fotodetectores comercialmente disponíveis, a implementação de circuitos de gerenciamento é capaz de fortalecer a robustez das medidas, criando um aparato com mais recursos em aplicações específicas. Duas aplicações práticas dessa hipótese são apresentadas em contextos diferentes, Criptografia Quântica e Monitoramento de Fibras Ópticas fazendo uso da plataforma FPGA. / [en] Despite the high sensitivity reached by Photon Detectors so far, the implementation of a background managing system often enforces the robustness of measurements thus creating a resourceful apparatus for specific applications. In this document, the management tools offered by Software Defined Hardware (SDHs) is put to test. By associating the power of FPGAs and Photon Detectors, enhanced measurement stations were assembled. Two different applications, a Bell State Projection Analysis Station and a Photon Counting Optical Time Domain Reflectometry (v-OTDR)Automatic Setup, are presented. Even though both experiments involve the detection of single photons, the background technologies differ drastically.

<p>The visible light photon counter (VLPC) is a high quantum efficiency (QE), Si-based, single-photon detector with high gain, low-noise multiplication, low timing jitter, and photon number resolution. While the VLPC has high QE in the visible wavelengths, the QE in the ultraviolet and infrared is low due to minimal absorption within the active layers of the device. In the ultraviolet, the absorption coefficient of Si is high and most of the incident photons are absorbed within the top contact of the device, whereas, in the infrared, Si is practically transparent. A number of applications in quantum information science would benefit from use of the VLPC if the QE was improved in the ultraviolet (e.g., state detection of trapped ions) and the infrared (e.g., long-distance quantum cryptography). This thesis describes the development of the ultraviolet photon counter (UVPC) and the infrared photon counter (IRPC), which are modified versions of the VLPC with increased QE in the ultraviolet and infrared wavelengths, respectively. The UVPC has a transparent metal Schottky contact to reduce absorption within the top contact of the VLPC, resulting in an increase in the QE in the ultraviolet by several orders of magnitude. The IRPC is a proposed device that has an InGaAs absorption layer that is wafer-fusion bonded to the VLPC. The band alignment of the resulting InGaAs/Si heterojunction is measured and shows a large discontinuity in the valence band that impedes carrier transport at the interface. A ultra-high vacuum wafer-bonding system was developed to understand the impact of the surface chemistry of the bonded wafers on the band alignment of the InGaAs/Si heterojunction of the IRPC.</p> / Dissertation

No description available.

Le projet CaLIPSO (Calorimètre Liquide Ionisation Position Scintillation Organométallique) a pour ambition de mettre au point un détecteur de γ 511 keV très efficace et très rapide pour la tomographie par émission de positons. Pour cela nous utilisons comme milieu de détection un nouveau liquide, le TMBi (TriMéthylBismuth). Dans le TMBi, l’interaction de photons γ produit des photons optiques et des paires électrons-ions. Le but de cette thèse est de mesurer les paramètres d’ionisation du TMBi et de construire, un détecteur de charge instrumentant efficacement ce liquide, et son électronique associée. Afin de pouvoir détecter les électrons libres créés par l’ionisation du liquide, celui-ci doit être ultrapur, c’est-à-dire débarrassé de tout composé électronégatif qui pourraient capturer les électrons et diminuer le signal. Ceci a été travaillé à l’aide de tamis moléculaires. Les signaux à détecter sont très faibles (fA, fC). Ainsi, l’environnement de l’expérience et le détecteur ont été développés pour des mesures très bas bruit (niveaux de bruit mesurés inférieurs à 10 fA et 200 électrons). Nous avons travaillé à mesurer le rendement d’ionisation (ou Gfi) qui quantifie le rendement de production de charge dans le liquide, la mobilité des électrons dans le TMBi et la résolution en énergie du détecteur. Ce sont les principaux paramètres permettant de valider l’utilisation de TMBi pour l’imagerie TEP. Les futurs développements comprennent la mise en œuvre d’un détecteur densément pixellisé et l’optimisation de la résolution en énergie. / The CALIPSO project (Calorimètre Liquide Ionisation Position Scintillation Organométallique) aims to develop a very efficient and very fast 511 keV γ detector for positron emission tomography. For this we use an organometallic liquid for the detection medium, the TMBi (TriMéthylBismuth). In TMBi, the interaction of a γ photon produces optical photons and electron-ion pairs.The aim of this thesis is to measure the ionization parameters of the liquid TMBi and build an efficient charge detector and its associated electronics.In order to detect the free electrons created by the ionization in the liquid, this liquid must be highly pure (which means free of any electronegative compound which could capture electrons and reduce the signal). This has been worked on using molecular sieves.The signals to be detected are very weak (fA, fC). Thus, the test setup and detector were developed for very low noise measurements (measured noise levels below 10 fA and 200 electrons).We measured the ionization yield (or Gfi) which quantifies the charge production yield in the liquid, the electrons mobility in the TMBi and the energy resolution of the detector. These are the main parameters to validate the use of TMBi for PET imaging.Future developments include the implementation of a pixelated detector and optimization of the detector energy resolution.

No description available.

<p>This doctoral thesis summarizes research in quantum cryptography done at the Department of Electronics and Telecommunications at the Norwegian University of Science and Technology (NTNU) from 1998 through 2007.</p><p>The opening parts contain a brief introduction into quantum cryptography as well as an overview of all existing single photon detection techniques for visible and near infrared light. Then, our implementation of a fiber optic quantum key distribution (QKD) system is described. We employ a one-way phase coding scheme with a 1310 nm attenuated laser source and a polarization-maintaining Mach-Zehnder interferometer. A feature of our scheme is that it tracks phase drift in the interferometer at the single photon level instead of employing hardware phase control measures. An optimal phase tracking algorithm has been developed, implemented and tested. Phase tracking accuracy of +-10 degrees is achieved when approximately 200 photon counts are collected in each cycle of adjustment. Another feature of our QKD system is that it uses a single photon detector based on a germanium avalanche photodiode gated at 20 MHz. To make possible this relatively high gating rate, we have developed, implemented and tested an afterpulse blocking technique, when a number of gating pulses is blocked after each registered avalanche. This technique allows to increase the key generation rate nearly proportionally to the increase of the gating rate. QKD has been demonstrated in the laboratory setting with only a very limited success: by the time of the thesis completion we had malfunctioning components in the setup, and the quantum bit error rate remained unstable with its lowest registered value of about 4%.</p><p>More than half of the thesis is devoted to various security aspects of QKD. We have studied several attacks that exploit component imperfections and loopholes in optical schemes. In a large pulse attack, settings of modulators inside Alice's and Bob's setups are read out by external interrogating light pulses, without interacting with quantum states and without raising security alarms. An external measurement of phase shift at Alice's phase modulator in our setup has been demonstrated experimentally. In a faked states attack, Eve intercepts Alice's qubits and then utilizes various optical imperfections in Bob's scheme to construct and resend light pulses in such a way that Bob does not distinguish his detection results from normal, whereas they give Bob the basis and bit value chosen at Eve's discretion. Construction of such faked states using several different imperfections is discussed. Also, we sketch a practical workflow of breaking into a running quantum cryptolink for the two abovementioned classes of attacks. A special attention is paid to a common imperfection when sensitivity of Bob's two detectors relative to one another can be controlled by Eve via an external parameter, for example via the timing of the incoming pulse. This imperfection is illustrated by measurements on two different single photon detectors. Quantitative results for a faked states attack on the Bennett-Brassard 1984 (BB84) and the Scarani-Acin-Ribordy-Gisin 2004 (SARG04) protocols using this imperfection are obtained. It is shown how faked states can in principle be constructed for quantum cryptosystems that use a phase-time encoding, the differential phase shift keying (DPSK) and the Ekert protocols. Furthermore we have attempted to integrate this imperfection of detectors into the general security proof for the BB84 protocol. For all attacks, their applicability to and implications for various known QKD schemes are considered, and countermeasures against the attacks are proposed.</p><p>The thesis incorporates published papers [J. Mod. Opt. 48, 2023 (2001)], [Appl. Opt. 43, 4385 (2004)], [J. Mod. Opt. 52, 691 (2005)], [Phys. Rev. A 74, 022313 (2006)], and [quant-ph/0702262].</p>

This doctoral thesis summarizes research in quantum cryptography done at the Department of Electronics and Telecommunications at the Norwegian University of Science and Technology (NTNU) from 1998 through 2007. The opening parts contain a brief introduction into quantum cryptography as well as an overview of all existing single photon detection techniques for visible and near infrared light. Then, our implementation of a fiber optic quantum key distribution (QKD) system is described. We employ a one-way phase coding scheme with a 1310 nm attenuated laser source and a polarization-maintaining Mach-Zehnder interferometer. A feature of our scheme is that it tracks phase drift in the interferometer at the single photon level instead of employing hardware phase control measures. An optimal phase tracking algorithm has been developed, implemented and tested. Phase tracking accuracy of +-10 degrees is achieved when approximately 200 photon counts are collected in each cycle of adjustment. Another feature of our QKD system is that it uses a single photon detector based on a germanium avalanche photodiode gated at 20 MHz. To make possible this relatively high gating rate, we have developed, implemented and tested an afterpulse blocking technique, when a number of gating pulses is blocked after each registered avalanche. This technique allows to increase the key generation rate nearly proportionally to the increase of the gating rate. QKD has been demonstrated in the laboratory setting with only a very limited success: by the time of the thesis completion we had malfunctioning components in the setup, and the quantum bit error rate remained unstable with its lowest registered value of about 4%. More than half of the thesis is devoted to various security aspects of QKD. We have studied several attacks that exploit component imperfections and loopholes in optical schemes. In a large pulse attack, settings of modulators inside Alice's and Bob's setups are read out by external interrogating light pulses, without interacting with quantum states and without raising security alarms. An external measurement of phase shift at Alice's phase modulator in our setup has been demonstrated experimentally. In a faked states attack, Eve intercepts Alice's qubits and then utilizes various optical imperfections in Bob's scheme to construct and resend light pulses in such a way that Bob does not distinguish his detection results from normal, whereas they give Bob the basis and bit value chosen at Eve's discretion. Construction of such faked states using several different imperfections is discussed. Also, we sketch a practical workflow of breaking into a running quantum cryptolink for the two abovementioned classes of attacks. A special attention is paid to a common imperfection when sensitivity of Bob's two detectors relative to one another can be controlled by Eve via an external parameter, for example via the timing of the incoming pulse. This imperfection is illustrated by measurements on two different single photon detectors. Quantitative results for a faked states attack on the Bennett-Brassard 1984 (BB84) and the Scarani-Acin-Ribordy-Gisin 2004 (SARG04) protocols using this imperfection are obtained. It is shown how faked states can in principle be constructed for quantum cryptosystems that use a phase-time encoding, the differential phase shift keying (DPSK) and the Ekert protocols. Furthermore we have attempted to integrate this imperfection of detectors into the general security proof for the BB84 protocol. For all attacks, their applicability to and implications for various known QKD schemes are considered, and countermeasures against the attacks are proposed. The thesis incorporates published papers [J. Mod. Opt. 48, 2023 (2001)], [Appl. Opt. 43, 4385 (2004)], [J. Mod. Opt. 52, 691 (2005)], [Phys. Rev. A 74, 022313 (2006)], and [quant-ph/0702262].

Inverse photoemission spectroscopy (IPES) is utilized for determining the unoccupied electron states of materials. It is a complementary technique to the widely used photoemission spectroscopy (PES) as it analyzes what PES cannot, the states above the Fermi energy. This method is essential to investigating the structure of a solid and its states. IPES has a broad range of uses and is only recently being utilized. This thesis describes the setup, calibration and operation of an IPES experiment. The IPES setup consists of an electron gun which emits electrons towards a sample, where photons are released, which are measured in isochromat mode via a photon detector of a set energy bandwidth. By varying the electron energy at the source, a spectrum of the unoccupied density of states can be obtained. Since IPES is not commonly commercially available the design consists of many custom made components. The photon detector operates as a bandpass filter with a mixture of acetone/argon and a CaF2 window setting the cutoff energies. The counter electronics consist of a pre-amplifier, amplifier and analyzer to detect the count rate at each energy level above the Fermi energy. Along with designing the hardware components, a Labview program was written to capture and log the data for further analysis. The software features several operating modes including automated scanning which allows the user to enter the desired scan parameters and the program will scan the sample accordingly. Also implemented in the program is the control of various external components such as the electron gun and high voltage power supply. The new setup was tested for different gas mixtures and an optimum ratio was determined. Subsequently, IPES scans of several sample materials were performed for testing and optimization. A scan of Au was utilized for the determination of the Fermi edge energy and for comparison to literature spectra. The Fermi edge energy was then used in a measurement of indium tin oxide (ITO) determining the conduction band onset. This allowed the determination of the "transfer gap" of ITO. Future experiments will allow further application of IPES on materials and interfaces where characterization of their electronic structure is desired.