Low-cost CW-LFM radar sensor at 100 GHz

This paper presents a W-band high-resolution radar sensor for short-range applications. Low-cost technologies have been properly selected in order to implement a versatile and easily scalable radar system. A large operational bandwidth of 9 GHz, required for obtaining high-range resolution, is attained by means of a frequency multiplication-based architecture. The system characterization to identify the performance-limiting stages and the subsequent design optimization are presented. The assessment of system performance for several representative applications has been carried out

Laser Pulses

This book discusses aspects of laser pulses generation, characterization, and practical applications. Some new achievements in theory, experiments, and design are demonstrated. The introductive chapter shortly overviews the physical principles of pulsed lasers operation with pulse durations from seconds to yoctoseconds. A theory of mode-locking, based on the optical noise concept, is discussed. With this approximation, all paradoxes of ultrashort laser pulse formation have been explained. The book includes examples of very delicate laser operation in biomedical areas and extremely high power systems used for material processing and water purification. We hope this book will be useful for engineers and managers, for professors and students, and for those who are interested in laser science and technologies

Addressed coherent manipulation of quantum bits encoded in strontium ions

In recent years, we have witnessed a significant growth in the field of quantum computing. Efforts on the experimental side are directed towards obtaining a fully-functional, large-scale quantum computer that obeys DiVincenzo's criteria, and the true capabilities of such a machine are not yet fully known. Similar to such a machine that can be programmed as wished, a quantum simulator can be initialised to solve quantum mechanical problems, by evolving and measuring the state of the qubits used. This is the framework in which this thesis project, at the Trapped Ion Quantum Technologies group at Stockholm University, takes place. The work concerns a quantum simulator based on a linear Paul trap, which confines 88Sr+ ions in a well-defined region of space. The goal is to design, simulate, and build an optical setup capable of addressing single ions with the 674 nm laser, and to perform single-qubit, multi-qubit and entangling operations on a few-qubit ion string.In recent years, we have witnessed a significant growth in the field of quantum computing. Efforts on the experimental side are directed towards obtaining a fully-functional, large-scale quantum computer that obeys DiVincenzo's criteria, and the true capabilities of such a machine are not yet fully known. Similar to such a machine that can be programmed as wished, a quantum simulator can be initialised to solve quantum mechanical problems, by evolving and measuring the state of the qubits used. This is the framework in which this thesis project, at the Trapped Ion Quantum Technologies group at Stockholm University, takes place. The work concerns a quantum simulator based on a linear Paul trap, which confines 88Sr+ ions in a well-defined region of space. The goal is to design, simulate, and build an optical setup capable of addressing single ions with the 674 nm laser, and to perform single-qubit, multi-qubit and entangling operations on a few-qubit ion string

Coherent and Incoherent Dynamics of Quasiparticles in Monolayer Molybdenum Diselenide

Monolayer Materials, especially single-layer graphite, called graphene, as the first synthesized and most prominent representative, have attracted significant research interest since its discovery in 2004. The efforts were rewarded with a Nobel prize in 2010 for the discovery of graphene, the same year in which the first monolayer transition metal dichalcogenide (ML-TMD) was found to have a direct bandgap. In contrast to graphene ML-TMDs have a direct bandgap in the visible or near-infrared spectral range, making them ideally suited for optoelectronic device applications. Explicit inversion symmetry breaking of the unit cell in ML-TMDs furthermore leads to a new interesting property, called valley pseudo-spin. Electrons excited within one valley are restricted to this valley due to momentum trapping. Investigating the valley pseudo-spin dynamics is of importance for both understanding of the fundamental physics as well as device applications since the valley pseudo-spin is a potential information carrier and has potential use for information storage or computing application. Additionally, the confinement to two dimensions leads to enhanced Coulomb interaction and increased dielectric screening between electron and hole. Interestingly, the two-dimensional screening effects were already studied before the first two-dimensional materials were synthesized on quasi-two-dimensional systems. The screening of the Coulomb interaction in turn leads to a significantly increased binding energy between electron and hole, such that the bound electron-hole state, so-called exciton, is stable up to room temperature and above. The same reasoning leads to an enhanced stability of charged excitons, so-called trions, which are the main focus of this dissertation. The optical response of ML-TMDs is therefore completely dominated by excitons and trions, requiring an in-depth understanding of these quasiparticles for device performance optimization. Time-resolved techniques can offer rich information compared to steady-state measurements. While steady-state measurements can resolve things such as the bandgap of a semiconductor or the fact that valley spin exists, time-resolved techniques allow the access of transients and reveal the lifetime of unstable or metastable states, which may be invisible in steady-state measurements. Coherent techniques are known for their ability of probing many-body effects and microscopic inhomogeneity. The technique used to investigate the coherent trion dynamics in this dissertation is two-dimensional coherent spectroscopy, a nonlinear coherent technique, that resolves the signal as a function of two time delays. Using two-dimensional spectroscopy, it is possible to measure the homogeneous linewidth, which is related to the coherence time, even in a strongly inhomogeneously broadened system. The measurement of the coherence time marks the first step in evaluating a material for possible quantum computation applications

Modelocking the bounce geometry laser

Imperial Users onl

Theoretical and Experimental Studies of Laser Induced Cooling of Solids

La plupart des recherches en technologies de réfrigération se concentrent dans l’amélioration de l’efficacité énergétique des réfrigérateurs et climatiseurs avides d’énergie, tandis qu’une petite fraction de la recherche est dédiée à la miniaturisation et à la flexibilité. La demande accrue pour des outils précis pour des mesures et fabrications générales, ainsi que la production, le traitement et la transmission de données, repoussent les limites de dispositifs électroniques et photoniques. Ces dispositifs nécessitent une gestion thermique qui n’est pas toujours possible d'atteindre avec les méthodes conventionnelles de réfrigération, en raison de la nécessité de miniaturisation, du transport thermique à distance et dans l’espace précis, l'insensibilité aux rayonnements électromagnétiques et des vibrations mécaniques ainsi que des capacités cryogéniques. Une technologie qui pourrait répondre à ces exigences est le refroidissement optique, où la chaleur est convertie en rayonnement optique, à travers un processus optique. Plusieurs segments de l’industrie moderne, ainsi que de la vie quotidienne, sont dépendants de la technologie laser. Cette large dépendance pousse le besoin de plus petits et plus puissants lasers pour les télécommunications, la recherche, les applications militaires, médicales et d’affichage, pour ne citer que quelques-uns. Le premier goulot d’étranglement pour la montée en puissance des lasers est dû à la production de chaleur, et la gestion thermique externe ne résout qu’une partie du problème, puisque les gradients thermiques – qui produisent des effets lenticulaires – sont encore présents. Etant donné que le refroidissement optique peut fournir une gestion thermique in situ, il peut être utilisé pour éliminer ces gradients thermiques nuisibles. Actuellement, le besoin d'efficacité énergétique est le moteur du changement de la technologie d'éclairage vers les diodes électroluminescentes (DELs). Les DELs souffrent cependant de génération de chaleur due à l’extraction limitée de la lumière et des pertes résistives, qui diminuent considérablement la durée de vie de ces émetteurs à semi-conducteurs. Ils ont donc besoin des échangeurs de chaleur relativement grands, qui à leur tour rendent difficile la miniaturisation. Le refroidissement par laser pourrait offrir une solution potentielle pour la gestion de la chaleur dans cette application, ainsi que pour des applications électroniques d’haute vitesse et pour des composants optiques de la prochaine génération d’ordinateurs, dans lequel une gestion de chaleur similaire est également nécessaire.----------Abstract Most research in refrigeration technologies concentrate in improving the energy efficiency of the energy-hungry refrigerators and air-conditioners, while a small fraction of the research is dedicated to the miniaturization and flexibility. Increased demand for precise tools for general measurement and manufacturing, as well as the generation, processing and transmission of data, push the limits of electronic and photonic devices. These devices require thermal management which is not always possible to achieve with conventional refrigeration methods, due to the need for miniaturization, remote or localized thermal transport, insensitivity to electromagnetic radiation and mechanical vibrations and cryogenic capabilities. One technology that could meet these requirements is optical cooling, where heat is carried away through optical radiation, through an optically-driven process. Many segments of modern industry, as well as everyday life, are dependent on lasers. This broad dependence has pushed the need for smaller and more powerful lasers for telecommunications, research, military, energy, medical, and display applications, to cite a few. The first bottleneck for power scaling of lasers is due to heat generation, and external thermal management solves only part of the problem since thermal gradients – which produce lensing effects – are still present. Since optical cooling can provide in-situ thermal management, it can be used to remove these deleterious thermal gradients. Currently, the need for energy efficiency is driving lighting technology towards light-emitting diode (LED) lighting. LEDs however suffer from heat generation due to limited light extraction and resistive losses, which severely decrease the lifetime of these semiconductor emitters. Thus they require relatively large heat exchangers, which in turn make miniaturization challenging. Laser cooling could offer a potential solution for heat management in this application as it could for high speed electronics applications and next-generation-computer optical components, in which similar heat management is also needed. Remote, compact and free-of vibration refrigeration provided by optical cooling can benefit satellites, which have the operation lifetime partially determined by the amount of cryogen they carry to refrigerate their detectors. The same characteristics benefit ultra-stable earth-based detectors, for example laser cavities for gravitational wave detection, in which stability is currently limited by the vibrations of their refrigeration system. All these problems have several different aspects, but one in common is that they cannot be readily solved with standard refrigeration technology, mainly due to the difficulties of remote and spatially-specific efficient transport of thermal energy