The goal of this project was to develop a measuring method and software code to determine and compare the focal ratio degradation of optical fibers for two different coupling technologies. One of the couplings used a fusing technology to splice the fiber, and the other coupling used a refractive index matching technology. Also, an optical fiber without any cleaving or splicing was used as a reference. A collimated beam test was developed as a method for measuring the focal ratio degradation for these different fiber couplings, and a software code was developed to process the results of the experiment. Using the collimated beam test and software code, the focal ratio degradation was calculated and compared between the couplings, and the results clearly stated that the reference fiber had the least focal ratio degradation. The fusing technology used for splicing the fiber had in comparison the least focal ratio degradation of the two different coupling technologies. The results were as expected and therefore the developed measuring method and software were estimated to have been carried out successfully. However, improvements to the measuring method and parts of the software could be done, especially regarding the background light which was a substantial source of error. In conclusion, the goal of the project was reached. / Inom astronomisk forskning används ofta optiska fibrer som informationslänk mellan teleskop och mätinstrument, eftersom de bidrar till att mätningar blir mer tillförlitliga då vibrationer och yttre miljöfaktorer får en mindre påverkan på resultaten. Inom detta projekt undersöktes ett par olika kopplingar av optiska fibrer och deras ljusförluster inom benämningen FRD (Focal ratio degradation). En mätmetod utvecklades tillsammans med en mjukvara som användes för nödvändiga beräkningar och analyser som ledde till att FRD kunde bestämmas. Metoden som användes kallas collimated beam test och innebar att parallellt ljus skickades in i ena fiberänden, vilket genererade en ring av ljus från den andra fiberänden. Mätningarna utfördes på tre olika fiber: en fiber var klyvd och sedan sammansmält, en annan fiber var klyvd och sedan ihopkopplad med hjälp av en vätska av matchande refraktionsindex och den tredje fibern var inte klyvd och fungerade som referens. Resultaten givna av mätningarna och mjukvaran var som man hade förväntat sig; FRD var minst för referensfibern och som högst för fibern med en koppling där refraktionsindex-matchande vätska användes. Även om det finns goda möjligheter att utveckla och förbättra mätmetoden, påvisades ett godtagbart resultat och målet med projektet ansågs därför vara uppnått.

Les travaux réalisés dans le cadre de cette thèse ont consisté en la réalisation d'un système de détection non destructif assisté par cavité d'atomes piégés sur réseau optique pour l'amélioration de la stabilité d'une horloge optique au strontium. La caractérisation de ce système dans son fonctionnement en régime classique, dans lequel les atomes piégés diffusent suffisamment peu de photons pour ne pas être expulsés du piège durant la détection, a mis en évidence des améliorations significatives en termes de rapport signal à bruit avec un gain d'un facteur cent en comparaison avec le système précédent de détection par fluorescence. Les gains en termes de stabilité par réduction de l'effet Dick restent cependant à concrétiser.Pour la réalisation du régime quantique, dans lequel moins d'un photon est diffusé par atome durant la détection, des idées nouvelles et des changements significatifs ont du être opérés sur le système et un travail théorique conséquent a été entrepris afin de déterminer la stratégie permettant une amélioration de la stabilité par réduction du bruit de projection quantique par mesure sans démolition de la cohérence de l'état interne atomique.J'y ai également aborder l'étude des effets des collisions chaudes des atomes de strontium piégés avec les particules du fond de vide résiduel, permettant une amélioration de l'exactitude de l'horloge. Cette thèse rapporte en particulier la première mesure expérimentale du déplacement de la fréquence de transition d'horloge due à ces collisions ainsi que son étude théorique. / The work achieved in the frame of this PhD training consisted in the implementation of a cavity enhanced non destructive detection system of atoms trapped in an optical lattice aiming at improving the stability of an optical strontium clock.The characterization of the system in its classical regime, for which a sufficiently low number of photons are scattered per atom to avoid expelling them off the trap, highlighted significant improvements in term of signal to noise ratio, with gain factor around 100 compared with the previously used fluorescence scheme. Yet, gains in terms of stability via Dick effect reduction still have to be demonstrated.Regarding the quantum regime, for which less than one photon is scattered per atom over the detection, new ideas and significant changes have been carried out on the system and a theoretical study was has been undertaken to determine the strategy for the improvement of the clock stability by quantum projection noise reduction via quantum non demolition measurement.It was as well the opportunity to study the effect of the hot collisions between the trapped strontium atoms and the residual vacuum background gas particles, allowing for the improvement of the clock uncertainty. This work reports in particular on the first measurement of strontium clock hot collisions shifts as well as its theoretical study.

Halide perovskite semiconductor nanocrystals have been studied a lot recently because they allow a precise control over the entire visible emission spectrum and as a result, the possibility of a variety of light-emitting applications. In this study, cesium lead bromide CsPbBr3 and cesium lead iodide CsPbI3 nanoplatelets of 3, 4 and 5 monolayers (ML) have been synthesized. The absorbance and emission of each solutions and monolayer are measured and analyzed in terms of the change in excitonic nature. The results show that the exciton peak decreases with the number of monolayers with a stronger excitonic behavior in the Bromide system in comparison to the Iodine perovskite with nearly no excitonic feature for the 5 ML system. An analysis of the apparent Stokes-shift show that it increases with the number of monolayer for CsPbBr3 in comparison with the Iodide system where it decreases. The vibrational properties were quantified with Raman spectroscopy and showed that a second signifying peak of the perovskite vibration change upon quantum confinement.

Quantum mechanics has played a big role in the development of our understanding of the smallest things in the universe. It has provided descriptions for phenomena like single electrons or single photons, which are single particles of light. One of the most mysterious properties of quantum systems is the ability to behave as a particle or a wave. In 1978, J. A. Wheeler devised an experiment to investigate if a quantum system knows in advance if it should propagate as a wave or as a particle through an experiment, by changing the experiment after the quantum system has entered the experimental set-up.  Here an optical all-in fiber platform for a Wheeler's delayed choice experiment is modeled, constructed and tested using commercially available fiber optic components. This is in contrast to previous delayed choice experiments, which have used free-space components in some parts of their experimental set-up. The optical set-up was modeled and simulated using a quantum formalism, with future work in mind if the platform is used to perform a quantum delayed-choice experiment. The platform used a Sagnac interferometer as the second beamsplitter in a Mach-Zehnder interferometer, to perform the choice of measuring either particle or wave properties. Using a fiber platform, the length of the platform can easily be extended with more fiber to accommodate a large separation between the beamsplitter in the beginning of the set-up, and the Sagnac interferometer at the end of the set-up. The result was a stable platform to measure particle behavior of light with good performance, and the ability to switch between these measurements on the fly. The system was tested with classical light, but the light source can be changed from a laser, to for example an attenuated laser, to enter the quantum domain for performing a quantum delayed-choice experiment using the platform. / Kvantmekaniken har inneburit stora genombrott i vår förståelse av de allra minsta tingen i universum. Kvantmekaniken har gett oss beskrivningar av fenomen som enstaka elektroners beteende eller enstaka ljuspartiklar, så kallade fotoner. En av de märkligaste egenskaperna som finns hos subatomära partiklar är förmågan att upptärda som en våg eller som en partikel, beroende på sammanhanget. År 1978 beskrev J. A. Wheeler ett experiment för att undersöka om en kvantmekanisk partikel, till exempel en foton, vet i förväg om den skall färdas som en partikel eller som en våg genom en experimentuppställning. Undersökningen av detta görs genom att ändra experimentuppställningen samtidigt som den kvantmekaniska partikeln färdas genom uppställningen.  En fiberoptisk plattform för Wheelers experiment med sent val modelleras, byggs med kommersiella fiberoptiska komponenter och testas i denna uppsats. Detta skiljer sig från tidigare experiment som har använt frirymds optik i någon del av experimentuppställningen. Den optiska kretsen modelleras med kvantmekanikens formalism, detta för att underlätta för framtida experiment som använder plattformen för att genomföra den kvantmekaniska varianten av Wheelers experiment med sent val.  Plattformen består av en Sagnac interferometer som ersätter den andra stråldelaren i en Mach-Zehnder interferometer, och därmed ger funktionen att kunna byta mellan mätning av partikelegenskaper och mätning av vågegenskaper. Den fiberoptiska plattformen är enkel att förlänga för att skapa ett långt avstånd mellan den första stråldelaren och Sagnac interferometern. Resultatet var en stabil plattform med god förmåga att mäta partikelegenskaper respektive vågegenskaper hos ljus och byta mellan dessa mätlägen under experimentets gång. Systemet testades med klassikt laserljus men denna ljuskälla kan enkelt bytas ut mot en dämpad laser för att komma ned på ljusnivåer med enstaka fotoner, och därmed kunna genomföra den kvantmekaniska varianten av Wheelers experiment med sent val.

When graphene is subjected to magnetic fields, it can be used as an optical device with light in the terahertz region. The functionality of the graphene depends on which magnetic field profile is influencing it. In this project, magnet configurations producing uniform and quadratic magnetic field profiles were studied. A script was written that allowed the user to place dipoles and ring magnets in the proximity of a graphene disc. The script would then determine the necessary dimensions of the permanent magnets used to produce the target magnetic field. The resulting magnetic configurations have been shown to produce a magnetic field within ±1% of the target profile, on the specified domain. However, further studies are required to establish if the acquired configurations proves reasonable in practise, and if so, how well the corresponding optical devices will perform.

Theoretical and experimental studies on intense laser atom interaction have drawn many interests over the past few decades. In this thesis, we consider strong-field tunnel ionization to explore two different problems dealing with the ionized-electron dynamics in the presence of an infrared, high-intensity, elliptically-polarized laser pulse. In the first part, we discover the electron dynamics from a static potential, this describes the complicated field-driven dynamics by a simple time-independent problem. In the second part, we set up an analytical expression for the attoclock offset angle. We use the time-dependent Kramers-Henneberger (KH) potential, and show how some approximations within the KH potential lead to the static potential and the analytical offset angle. We elucidate good agreement of our theory with the numerical results obtained from classical equations of motion. Finally, the comparison with the available experimental data has led to an interestingly new tunnel exit-radius different from the conventional models.

Low dimensional semiconductor structures are modeled using techniques from the field of many-body atomic physics. B-splines are used to create a one-particle basis, used to solve the more complex many-body problems. Details on methods such as the Configuration Interaction (CI), Many-Body Perturbation Theory (MBPT) and Coupled Cluster (CC) are discussed. Results from the CC singles and doubles method are compared to other high-precision methods for the circular harmonic oscillator quantum dot. The results show a good agreement for the energy of many-body states of up to 12 electrons. Properties of elliptical quantum dots, circular quantum dots, quantum rings and concentric quantum rings are all reviewed. The effects of tilted external magnetic fields applied to the elliptical dot are discussed, and the energy splitting between the lowest singlet and triplet states is explored for varying geometrical properties. Results are compared to experimental energy splittings for the same system containing 2 electrons.

The broad range of applications for photochemical reactions is the result of light-matter interaction at the electronic level. The diverse application of photochemistry in various fields, including photovoltaic materials, molecular switches, and biological systems are due to electronic and structural transformations induced by photoexcitation as well as molecular alteration due to electron and charge transfer. An improved understanding of these photochemical events is dependent on the fundamental theoretical evaluation, to model and analyze the ultrafast processes. The studies discussed in this thesis explore such theoretical implementation in two different frontiers. In the first study, dynamic simulations are performed to model the light-induced bond dissociation of phenyl azide. The surface hopping formalism, implemented under the semiclassical molecular dynamics approach helped in tracing the time evolution of the electronic and structural levels, involved in the photodissociation. In the second study, the time-dependent density functional theory has been applied to generate XA spectra of imidazole solutions. The theoretical assessments support experimental measurements and provide more insight into the core excitations and structural influence on the absorption spectra. / Fotokemiska reaktioner styrs av växelverkan mellan ljus of materia på en elektronisk nivå. I olika fält finns det vitt skilda tillämpningarna av fotokemi. Dessa inkluderar ljusinducerade processer i solceller, molekylära strömbrytare, och biologiska system. Reaktionerna beror av elektroniska och strukturella transformationer som induceras av fotoexcitationen, och kan ge upphov till energi- och laddningsöverföring. För att få utökad förståelse av fotokemiska reaktioner behövs grundläggande teoretiska studier där ultrasnabba processer modelleras och analyseras i jämförelse med experiment. Undersökningar som presenteras i denna avhandling använder sig att teoretiska modeller i två olika områden av fotokemi. I den första studien har vi genomfört dynamiska simuleringar för att modellera ljusinducerad dissociation av fenylazid. Vi have använt en semi-klassisk approximation med hopp mellan olika elektroniska tillstånd vilket gör det möjligt att följa utvecklingen i elektroniska och geometriska frihetsgrader under fotodissociationen. I den andra studien har tidsberoende täthetsfunktionalteori använts för att simulera röntgenabsorptionsspektrum för imidazol i lösning. Genom att utvärdera olika geometriska modeller med teoretiska beräkningar kan vi berika tolkningen av experimentella mätningar, och även få detaljerat insikt i innerskalsexcitationer och hur geometrin påverka röntgenspektrum.

In this study we have interviewed eight teachers about when and how particle concepts should be taught. All of the surveyed teachers argue for an early introduction. This view is also consistent with the scientists on when the particle concepts should be introduced. By an early introduction teachers and scientists consider the age between 6-12 years old. A majority of the scientists and the surveyed teachers use concept of change as a entery point to talk about particle ideas. A substance that is commonly used among both teachers and scientists is water. We can also find out that the surveyed teachers think that the particle concepts are fundamental for pupils to get a broader understanding in school science learning.

Wireless transmission is an everyday part of movie production and a tool many people use in their work. Work, on a movie production, is fast, intense, and varies in geographical location almost on a daily basis (sometimes several locations in a day). Despite this, the stream, the transmission, must hold so the crew can work. This thesis explores the different impacts materials have on the transmission (using the Boxx Atom System as a test object). The materials were everyday occurrences such as walls (wood and stone), doors (steel, wood), windows (glass), and humans (the crew). The tests were done in the office of Video Assist Sweden in Stockholm, testing both quality and calculating the link margin. The results gave room for improvement but were interesting and sometimes surprising. Glass is best for a smooth transmission. Wooden doors and human beings’ impact were basically the same and stone and steel had the largest impact. In this thesis, we attempt to explain the results and draw conclusions from them and our own experiences in the field. / Trådlös överföring är en vardaglig del av en filmproduktion och ett verktyg som många använder i sitt arbete. Arbetet med en filmproduktion är snabbt, intensivt och varierar mellan olika platser nästan dagligen (ibland flera platser på en dag). Trots detta måste video transmissionen fungera så att hela teamet kan arbeta effektivt. Detta examensarbete undersöker de olika effekterna material har på transmissionen (med hjälp av Boxx Atom System som testobjekt). Materialen var vardagliga händelser som väggar (trä och sten), dörrar (stål, trä), fönster (glas) och människor (besättningen). Testerna gjordes på Video Assist Swedens kontor i Stockholm, där man testade både kvalitet och beräknade länk-marginalen. Resultaten gav utrymme för förbättringar men var intressanta och ibland överraskande. Glas är bäst för en smidig överföring. Träs och människors påverkan var i princip densamma och sten och stål hade störst påverkan. I detta examensarbete försöker vi förklara resultaten och dra slutsatser från dem och våra egna erfarenheter inom området.