This report examines the cross sections of silver microresonators subjected to an incident light with different polarization. The microresonators had different geometries with and without broken symmetries. Cross section profiles for different microresonator configurations are interesting for the division of Material Physics, Uppsala University, when designing metamaterials to tune the optical response of the material. The goal is to form an insight of how the optical response can be tuned by choosing different geometries, varying the size and polarization of the incident light. In this project computer simulations in COMSOL were made to simulate the optical response of different microresonators. When the incident light interact with the silver microresonators plasmonic excitations is generated which in turn interacts with the light changing the phase and therefore the optical response. By increasing the radius of the disk silver microresonantors the resonance was found to shift to lower energies. For a geometry with a disk microresonator inside a ring microresonator the Fano resonances were dependent of the radius of the disk microresonator.

During the past decades, the development of laser technology has produced pulses with increasingly higher peak intensities. These can now be made such that their strength rivals, and even exceeds, the atomic potential at the typical distance of an electron from the nucleus. To understand the induced dynamics, one can not rely on perturbative methods and must instead try to get as close to the full machinery of quantum mechanics as practically possible. With increasing field strength, many exotic interactions such as magnetic, relativistic and higher order electric effects may start to play a significant role. To keep a problem tractable, only those effects that play a non-negligible role should be accounted for. In order to do this, a clear notion of their relative importance as a function of the pulse properties is needed.  In this thesis I study the interaction between atomic hydrogen and super-intense laser pulses, with the specific aim to contribute to the knowledge of the relative importance of different effects. I solve the time-dependent Schrödinger and Dirac equations, and compare the results to reveal relativistic effects. High order electromagnetic multipole effects are accounted for by including spatial variation in the laser pulse. The interaction is first described using minimal coupling. The spatial part of the pulse is accounted for by a series expansion of the vector potential and convergence with respect to the number of expansion terms is carefully checked. A significantly higher demand on the spatial description is found in the relativistic case, and its origin is explained. As a response to this demanding convergence behavior, an alternative interaction form for the relativistic case has been developed and presented. As a guide mark for relativistic effects, I use the classical concept of quiver velocity, vquiv, which is the peak velocity of a free electron in the polarization direction of a monochromatic electromagnetic plane wave that interacts with the electron. Relativistic effects are expected when vquiv reaches a substantial fraction of the speed of light c, and in this thesis I consider cases up to vquiv=0.19c. For the present cases, relativistic effects are found to emerge around vquiv=0.16c .

III-Nitride semiconductors are very promising in both electronics and optical devices. The ability of the III-Nitride semiconductors as light emitters to span the electromagnetic spectrum from deep ultraviolet light, through the entire visible region, and into the infrared part of the spectrum, is a very important feature, making this material very important in the field of light emitting devices. In fact, the blue emission from Indium Gallium Nitride (InGaN), which was awarded the 2014 Nobel Prize in Physics, is the basis of the common and important white light emitting diode (LED). Quantum dots (QDs) have properties that make them very interesting for light emitting devices for a range of different applications, such as the possibility of increasing device efficiency. The spectrally well-defined emission from QDs also allows accurate color reproduction and high-performance communication devices. The small size of QDs, combined with selective area growth allows for an improved display resolution. By control of the polarization direction of QDs, they can be used in more efficient displays as well as in traditional communication devices. The possibility of sending out entangled photon pairs is another QD property of importance for quantum key distribution used for secure communication. QDs can hold different exciton complexes, such as the neutral single exciton, consisting of one electron and one hole, and the biexciton, consisting of two excitons. The integrated PL intensity of the biexciton exhibits a quadratic dependence with respect to the excitation power, as compared to the linear power dependence of the neutral single exciton. The lifetime of the neutral exciton is 880 ps, whereas the biexciton, consisting of twice the number of charge carriers and lacks a dark state, has a considerably shorter lifetime of only 500 ps. The ratio of the lifetimes is an indication that the size of the QD is in the order of the exciton Bohr radius of the InGaN crystal making up these QDs in the InGaN QW. A large part of the studies of this thesis has been focused on InGaN QDs on top of hexagonal Gallium Nitride (GaN) pyramids, selectively grown by Metal Organic Chemical Vapor Deposition (MOCVD). On top of the GaN pyramids, an InGaN layer and a GaN capping layer were grown. From structural and optical investigations, InGaN QDs have been characterized as growing on (0001) facets on truncated GaN pyramids. These QDs exhibit both narrow photoluminescence linewidths and are linearly polarized in directions following the symmetry of the pyramids. In this work, the neutral single exciton, and the more rare negatively charged exciton, have been investigated. At low excitation power, the integrated intensity of the PL peak of the neutral exciton increases linearly with the excitation power. The negatively charged exciton, on the other hand, exhibits a quadratic power dependence, just like that of the biexciton. Upon increasing the temperature, the power dependence of the negatively charged exciton changes to linear, just like the neutral exciton. This change in power dependence is explained in terms of electrons in potential traps close to the QD escaping by thermal excitation, leading to a surplus of electrons in the vicinity of the QD. Consequently, only a single exciton needs to be created by photoexcitation in order to form a negatively charged exciton, while the extra electron is supplied to the QD by thermal excitation. Upon a close inspection of the PL of the neutral exciton, a splitting of the peak of just below 0.4 meV is revealed. There is an observed competition in the integrated intensity between these two peaks, similar to that between an exciton and a biexciton. The high energy peak of this split exciton emission is explained in terms of a remotely charged exciton. This exciton state consists of a neutral single exciton in the QD with an extra electron or hole in close vicinity of the QD, which screens the built-in field in the QD. The InGaN QDs are very small; estimated to be on the order of the exciton Bohr radius of the InGaN crystal, or even smaller. The lifetimes of the neutral exciton and the negatively charged exciton are approximately 320 ps and 130 ps, respectively. The ratio of the lifetimes supports the claim of the QD size being on the order of the exciton Bohr radius or smaller, as is further supported by power dependence results. Under the assumption of a spherical QD, theoretical calculations predict an emission energy shift of 0.7 meV, for a peak at 3.09 eV, due to the built-in field for a QD with a diameter of 1.3 nm, in agreement with the experimental observations. Studying the InGaN QD PL from neutral and charged excitons at elevated temperatures (4 K to 166 K) has revealed that the QDs are surrounded by potential fluctuations that trap charge carriers with an energy of around 20 meV, to be compared with the exciton trapping energy in the QDs of approximately 50 meV. The confinement of electrons close to the QD is predicted to be smaller than for holes, which accounts for the negative charge of the charged exciton, and for the higher probability of capturing free electrons. We have estimated the lifetimes of free electrons and holes in the GaN barrier to be 45 ps and 60 ps, in consistence with excitons forming quickly in the barrier upon photoexcitation and that free electrons and holes get trapped quickly in local potential traps close to the QDs. This analysis also indicates that there is a probability of 35 % to have an electron in the QD between the photoexcitation pulses, in agreement with a lower than quadratic power dependence of the negatively charged exciton. InN is an attractive material due to its infrared emission, for applications such as light emitters for communication purposes, but it is more difficult to grow with high quality and low doping concentration as compared to GaN. QDs with a higher In-composition or even pure InN is an interesting prospect as being a route towards increased quantum confinement and room temperature device operation. For all optical devices, p-type doping is needed. Even nominally undoped InN samples tend to be heavily n-type doped, causing problems to make pn-junctions as needed for LEDs. In our work, we present Mg-doped p-type InN films, which when further increasing the Mg-concentration revert to n-type conductivity. We have focused on the effect of the Mg-doping on the light emission properties of these films. The low Mg doped InN film is inhomogeneous and is observed to contain areas with n-type conductivity, so called n-type pockets in the otherwise p-type InN film. A higher concentration of Mg results in a higher crystalline quality and the disappearance of the n-type pockets. The high crystalline quality has enabled us to determine the binding energy of the Mg dopants to 64 meV. Upon further increase of the Mg concentration, the film reverts to ntype conductivity. The highly Mg doped sample also exhibits a red-shifted emission with features that are interpreted as originating from Zinc-Blende inclusions in the Wurtzite InN crystal, acting as quantum wells. The Mg doping is an important factor in controlling the conductivity of InN, as well as its light emission properties, and ultimately construct InN-based devices. In summary, in this thesis, both pyramidal InGaN QDs and InGaN QDs in a QW have been investigated. Novel discoveries of exciton complexes in these QD systems have been reported. Knowledge has also been gained about the challenging material InN, including a study of the effect of the Mg-doping concentration on the semiconductor crystalline quality and its light emission properties. The outcome of this thesis enriches the knowledge of the III-Nitride semiconductor community, with the long-term objective to improve the device performance of III-Nitride based light emitting devices.

Investigating and mapping fundamental processes in nature is a driving force for breakthroughs in research and technology. Doing so, requires knowledge of the smallest scales of the world. One way of performing measurements on these scales is through intense x-ray sources, which have improved greatly over the last decades. By combing these sources with state of the art optics, even higher flux densities can be reached, allowing for faster measurements and ground-breaking discoveries.  This study aims to explore the performance of polycapillary optics, when aligned to one of the most intense x-ray micro sources in the world, the liquid-metal-jet D2+. Knife edge scans were performed together with a photon-counting medipix x-ray camera to quantify focus properties such as, flux, flux density, transmission, gain and beam width. Measurements were conducted with a 20 μm source spot that was compared to a simulated 200 μm source spot, both at 260 W electron beam power. The data from vertical and horizontal scans were combined to reconstruct the 2D functionality of the polycapillary optic. The flux density were almost four times higher with the 20 μm spot compared to the simulated 200 μm spot. This result correlated with the condition for total external reflection and the local divergence. The conclusion is that the small source spot of the liquid-metal-jet source improves the efficiency of the polycapillary optic.  The efficiency could still be improved, if the deviation in the pointing accuracy could be minimized. Furthermore, the combination of liquid-metal-jet x-ray source and the polycapillary optic, achieved extremely high flux densities. This was specially compared to an x-ray source used for confocal micro XRF, where the flux was almost nine times higher with the liquid-metal-jet x-ray source. This allows for faster measurements within confocal micro XRF and other techniques demanding very high flux densities, but with low demands on beam divergence and spectral purity.

In this licentiate thesis the luminescence properties of two flexible conjugated dyes have been studied. The first, Pt1, is a platinum(II) acetylide chromophore used in optical power limiting materials. The second is a set of optical probes known as luminescent conjugated oligothiophenes (LCOs), which are used to detect and characterize the protein structures associated with amyloid diseases such as Alzheimer’s disease. MM3 and CHARMM force field parameters have been derived for the Pt1 chromophore and LCOs, respectively, based on potential energy surface references calculated at the density functional theory (DFT)/B3LYP level of theory. The parameters have been used to perform room temperature molecular dynamics simulations of the chromophores in solvent, where tetrahydrofuran was used for Pt1 and water for the LCOs. Conformationally averaged absorption spectra were obtained, based on response theory calculations at the time-dependent DFT(TDDFT)/CAM-B3LYP level of theory for a selection of structures from the simulations. For one of the LCOs, p-HTAA, force field parameters were also created describing the dominant first excited state, based on TDDFT/B3LYP reference potential energy surfaces. These were used for molecular dynamics simulations of the chromophore in the excited state, allowing the creation of an emission spectrum. A theoretically obtained Stokes shift of 112 nm could be computed based on the absorption and emission spectra, which is in good agreement with the experimental value of 124 nm. In addition, a quantum mechanics/molecular mechanics study of the effects of solvation on the absorption properties of the p-HTAA chromophore in water has been conducted, resulting in two models for including these effects in the averaged spectra. The first includes explicit water molecules in the form of point charges and polarizable dipole moments, and results in an absorption wavelength that is blueshifted by 2 nm from a high quality reference calculation. The second model involves the complete removal of the solvent as well as the ionic groups of the chromophore. The resulting absorption wavelength is blueshifted by an additional 4 nm as compared to the first model, but requires only one fifth of the computational resources.

The manufacturing of optical components, such as lenses or mirrors, consists of numeroussteps that are essential to the performance of the fnished optical system, such as the specifcation ofthe optical surface. For a longer period, the main focus has been in identifying and restricting thenegative effects of the low and high spatial frequency content of the surface. However, as technologyand optical equipment has become more advanced, the effects of the mid-spatial frequencies havebeen studied more, and continue to be a topic of research. As of now, there is still a need for methodsthat accurately predict and analyse the regime of mid-spatial frequencies, such that they can becontrolled during the specifcation phase, successfully limiting the need of post-processing steps.This work introduces a software tool, specifcally designed to approach this problem, which wasto be developed in Python as a contribution to the existing Optical Scripting Library at OHB. Byspecifying an optical component in terms of a Power Spectral Density function, together with thecontributions from different spatial frequency domains and the application of a ripple patterns, thissoftware tool can generate pseudo-random optical surfaces, which maintains the input specifcations.Furthermore, a Dynamic Link Library fle was developed, sharing the same functionality as thePython implementation, allowing for simulations using Zemax OpticStudio. Using the software tool,it was found that the relative error between input and output measurements were approximately0.78%, in terms of the Power Spectral Density Function. In addition, the result of analysing one of thetwo test cases indicate that the software tool is effective in predicting the infuence of mid-spatialfrequency errors, fulflling a previously measured predicition. The second test case proved that thesoftware tool can be used for mimicing surfaces of real measurements, holding the same specifcations.

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.

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.