This thesis describes the work performed at the Quantum Optics lab at UNAM,Mexico City. Third order spontaneous parametric down conversion (TOSPDC) isa quantum optical process where an incoming photon is annihilated and generatesthree quantum entangled photons, so called photon triplets, under energy and mo-mentum conservation. This TOSPDC process was experimentally realized using afused silica optical fiber as nonlinear source. The spectra of the emitted signal weremeasured and coincidence counts measurements were performed in order to verifythe generation of these triplets. An average of 0.8 triplets per second were detected,which is the first sign of a realized TOSPDC process to our knowledge. At thispoint, the signal was too low for any spectra to be recorded. There is a lot of roomfor improvements, especially regarding the equipment used due to the heavy signalloss throughout the experimental setup, and more experiments will be performed toproperly verify the production and entanglement of the triplet photons.

Quantification of spectral data is of great interest in many fields of science, since it can provide further insight into other properties of an object. However, traditional cameras are usually made to image the world in a similar fashion as to how we see it, wherefore they are usually not fit to record nor measure further spectral information. To get a better insight into the spectral properties of an object, a hyperspectral camera might be of use, since those can often identify and measure hundreds of different spectral bands. In this study we look at the construction and further development of an existing design of a push broom hyperspectral imaging system, built with optics for a fraction of the cost of commercial ones. With developed software and objects at hand a spectral calibration was performed, showing a possible spectral range of 184(2)-918(11) nm, but the use of the whole spectral range was however not possible due to limitations in the transmissivity of the lenses below 350 nm. A shift of the spectral range towards longer wavelengths is proposed, which would give further insight into the near infrared spectrum without any information losses. It was found that the spectral calibration of the imager was the main limiting factor of the system, since inaccuracies up to ±11 nm were identified, while the resolution has been found to be 1.4 nm in previous studies, proving that better calibrations are of essence. In good operating conditions, the resolution in the angle of view of the imager was found to be 0.55 mdeg. If the measurement conditions are not as good, or if such kind of spatial resolution is not required, a camera with a smaller detector size and larger pixels could be used to lower the cost of the system without a deterioration in image quality, since the uncertainties in the calibrations and measurement conditions were found to be the limiting factor.

In this thesis, periodic structures with higher symmetries symmetries are discussed. The main focus of the thesis is on twist symmetries. Importantly, the attractive properties of twist symmetries for the control of electromagnetic wave propagation are demonstrated. Furthermore, the additional degree of freedom offered by twist symmetries is used to design two microwave devices. A structure is twist-symmetric if its periodicity can be described by the geometrical operation consisting of a translation and a rotation around an axis. In this thesis, it is demonstrated that there are no stop-bands between the first q modes in the Brillouin diagram of a twist-symmetric structure, where q is the symmetry order. The importance of the symmetry to the absence or presence of stop-bands is illustrated by studying structures where the symmetry is gradually broken. Furthermore, it is demonstrated that a twist-symmetric structure can produce a higher and less dispersive effective refractive index, compared to a conventional periodic structure. These characteristics are attractive for the design of microwave devices. To provide insight into the physics of twist symmetry, a mode matching formulation is derived to analyze twist-symmetric coaxial transmission lines. The formulation is used to highlight the importance of higher order coupling on the response in structures with varying order of the twist symmetry.  In this thesis, we also discuss another type of symmetry; polar glide symmetry. A periodic structure possesses a polar glide symmetry if its periodicity can be described by the geometrical operation consisting of a translation and a reflection in a cylindrical surface. It is demonstrated that there is no stop-band between the first two modes in a polar glide structure, which is similar to what has been reported for Cartesian glide symmetry previously. Furthermore, twist symmetry and polar glide symmetry is combined into twisted polar glide symmetry. The effect of this combination on the stop-band between the second and third modes is demonstrated. It is concluded that this type of symmetry finds application in filter design. Finally, the additional design freedom offered by twist symmetry is used to produce two microwave components. A reconfigurable phase shifter is designed, where the phase delay in the phase shifter depends on the order of the twist symmetry. Furthermore, a flat lens is designed to transform a spherical wave into a quasi-planar wave. The focusing properties of the lens is obtained by locally varying the order of the symmetry throughout the lens aperture. / I denna avhandling diskuteras periodiska strukturer med högre symmetrier. Huvudfokus av avhandlingen är skruvsymmetrier. Vi visar de attraktiva egenskaperna av skruvsymmetrier för kontrollen av elektromagnetiska vågor. Dessutom används den extra designfriheten från skruvsymmetrier för att designa två mikrovågskomponenter. En struktur är skruvsymmetrisk om dess period kan beskrivas av en geometriska operation bestående av en translation och en rotation runt en axel. I denna avhandling visar vi att det inte finns några bandgap mellan de första q moderna i Brillouindiagrammet för en skruvsymmetrisk struktur, där q är symmetriordningern. Betydelsen av symmetri för frånvaron och närvaron av bandgap illustreras genom att studera strukturer där symmetrin gradvis bryts. Vidare visar vi att en skruvsymmetrisk struktur kan producera ett högre och mindre dispersivt effektivt refraktivt index jämfört med en vanlig periodisk struktur. Dessa egenskaper är attraktiva i designen av mikrovågskomponenter. För att ge insikt i fysiken bakom skruvsymmetrier tas en modmatchningsformulering fram för att studera skruvsymmetriska koaxiala transmissionsledare. Formuleringen används för att belysa vikten av högre ordnings vågkoppling för egenskaperena i strukturer med olika ordnings skruvsymmetri.  I denna avhandling diskuteras ytterliage en typ av högre symmetri; polär glidsymmetri. En struktur har en polär glidsymmetri om dess period kan beskrivas av en geometriska operation bestående av en translation och en spegling i en cylindrisk yta. Vi visar att det inte finns något bandgap mellan de två första moderna i en struktur med polär glidsymmetri, vilket också tidigare visats för Cartesisk glidsymmetri. Vidare kombinerar vi skruv- och polär glidsymmetri. Implikationerna av denna kombination på bandgapet mellan högre moder diskuteras. Vi kommer fram till att denna typ av kombinerad symmetri finner tillämpningar i filterdesign.  Slutligen används den extra designfriheten från skruvsymmetri för att designa två mikrovågskomponenter. En konfigurerbar fasskiftare designas, där fasskiftningen beror på symmetriordningen. Vidare designas en platt lins som omvandlar en sfärisk våg till en kvasiplan våg. Fokuseringsegenskaperna i linsen uppnås genom att lokalt variera symmetriordningen i linsens apertur. / <p>QC 20211103</p>

Calculation of number of photon pairs produced by type-I degenerate Spontaneous Parametric Down-Conversion inside a BBO crystal.

Today we are seeing exciting developments in the field of autonomous vehicles, on both software and hardware. Veoneer is a company making a contribution where research and manufacturing is being done on hardware and active safety. One of the most important aspects in this field is road safety, where understanding the behaviour of sensors used in vehicles is essential. From the point of view of safety, understanding how weather affects the sensors is necessary for a successful deployment. This study is a continuation of previous studies done at Veoneer, and regards how various adverse condition affect the performance of a short-range LiDAR and gives a thorough description of the involved physical processes. Data collected over a couple of months was analysed and compared to theoretical models in order to establish their validity. In addition, LiDAR measurement were done in a chamber where conditions could be varied in a controlled manner. Furthermore, analysis methods were used to transform the data into a form potentially more useful for use in machine learning algorithms to estimate the ability to classify conditions based on LiDAR signals. The used models showed mixed results, with some showing more agreement than others. Models regarding foggy conditions generally showed greater agreement with data than in other conditions, although some variation around the predictions did occur. In regards to the performance of the classification algorithms, there were als omixed results, where the sensitivity in fog was at most 96 % and the precision at most 64 %. This thesis also enables and suggests further research into the utility of short-range LiDAR both in the field of autonomous vehicle safety as well as in use of other fields such as meteorology.

Increasing global warming with droughts, forest fires and melting polar ice has forced the world to speed up the transition from fossil fuel to fossil free energy. A big part of it is the use of solar energy. To obtain solar thermal energy, different sorts of solar collectors have been developed. One of these are the parabolic solar collector, a trough which concentrates the sun rays onto a receiver tube, which in turn absorbs the thermal heat. Absolicon Solar Collector AB is a Swedish company developing a parabolic solar collector named T160. These collectors are optically verified in the end of the Absolicon production line to decide if they meet the expected criteria. The verification of the parabolic shape is of utmost importance for the performance of the trough while a shape error can cause the beam to hit the receiver tube in a sub-optimal angle or miss it completely. If this were to happen, all of the energy can not be extracted. Earlier research have developed different methods for finding slope errors, deviations in the normal angles, in the trough but does not investigate the connection between slope errors and the trough shape errors that might have caused the deviations. This report aims to develop an algorithm based on slope errors in a parabolic trough collector which identifies four predetermined common shape errors in the trough. Identifying shape errors help to quickly identify and correct systematic deviations. In addition, this work aims to implement a new acceptance criteria based on slope errors for the solar collectors to make sure they hold up to their standard. The algorithm should also be compatible with a new camera system being implemented in the optical verification at Absolicon. This is done by deriving mathematical expressions for the normal angles in the trough with respect to the shape errors. By using the Pinhole Camera Model, the Law of Reflection and geometric properties of the solar collector, it is possible to convert pixel coordinates of receiver tube edges in images to normal angles. The resulting deviation in normal angle compared to the ideal ones are analysed and fitted to the mathematically derived expression for the normal angles by a build in minimization method in the tool lmfit in Python which uses non-linear least squares to detect type shape errors. The acceptance criteria and compatibility with the new system is implemented and taken into account. The results show that the calculation of slope errors from the data is valid with an uncertainty of 0.82 mrad and expected differences in the acceptance criteria quality value is seen when dealing with solar collectors with different type shape errors. The type shape error algorithm finds the correct shape errors for noisy self-created data which shows that the method works. The results when testing on real collectors with forced shape errors show potential but is in need of further adjustments and more clean precise data to produce certain accurate results. The algorithm is a good start to create a tool for finding typical shape errors in parabolic solar collectors.

Quantum dots, also known as artificial atoms, are created by tightly confining electrons, and thereby quantizing their energies. They are important components in the emerging fields of nanotechnology where their potential uses vary from dyes to quantum computing qubits. Interesting properties to investigate are e.g. the existence of atom-like shell structures and lifetimes of prepared states. Stability and controllability are important properties in finding applications to quantum dots. The ability to prepare a state and change it in a controlled manner without it loosing coherence is very useful, and in some semiconductor quantum dots, lifetimes of up to several milliseconds have been realized. Here we focus on dots in semiconductor materials and investigate how the confined electrons are effected by their experienced potential. The shape of the dot will effect its properties, and is important when considering a suitable model. Structures elongated in one dimension, often called nanowires, or shaped as rings have more one-dimensional characteristics than completely round or square dots. The two-dimensional dots investigated here are usually modeled as harmonic oscillators, however we will also consider circular well models. The effective potential confining the electrons is investigated both in regard to how elliptical it is, as well as how results differ when using a harmonic oscillator or a circular well potential. By mixing spin states through spin-orbit interaction transitioning between singlet and triplet states becomes possible with spin independent processes such as phonon relaxation. We solve the spin-mixing two-electron problem numerically for some confinement, and calculate the phonon transition rate between the lowest energy singlet and triplet states using Fermi's golden rule. The strength of the spin-orbit interaction is varied both by changing the coupling constants, and by applying an external, tilted, magnetic field. The relation between magnetic field parameters and dot parameters are used to maximize state lifetimes, and to model experimental results. / <p>At the time of the doctoral defense, the following paper was unpublished and had a status as follows: Paper 3: Manuscript.</p>

Ultra-violet and visible light induced processes in small organic molecules play very important roles in many fields, e.g., environmental sciences, biology, material development, chemistry, astrophysics and many others. Thus it is of great importance to better understand the mechanisms behind these processes. To achieve this, a bottom-up approach is most effective, where the photo-induced dynamics occurring in the simplest organic molecule (ethylene) are used as a starting point. Simple substituents and functional groups are added in a controlled manner to ethylene, and changes in the dynamics are investigated as a function of these modifications. In this manner, the dynamics occurring in more complex systems can be explored from a known base. In this thesis, the excited state dynamics of small organic molecules are studied by a combination of time-resolved photoelectron spectroscopy and various computational methods in order to determine the basic rules necessary to help understand and predict the dynamics of photo-induced processes. The dynamics occurring in ethylene involve a double bond torsion on the ππ* excited state, followed by the decay to the ground state coupled with pyramidalization and hydrogen migration. Several different routes of chemical modification are used as the basis to probe these dynamics as the molecular complexity is increased. (i) When ethylene is modified by the addition of an alkoxyl group (-OCnH2n+1), a new bond cleavage reaction is observed on the πσ* state. When modified by a cyano (-CN) group, a significant change in the carbon atom involved in pyramidalization is observed. (ii) When ethylene used to build up small cyclic polyenes, it is observed that the motifs of the ethylene dynamics persist, expressed as ring puckering and ring opening. (iii) In small heteroaromatic systems, i.e., an aromatic ring containing an ethylene-like sub-structure and one or two non-carbon atoms, the type of heteroatom (N: pyrrole, pyrazole O: furan) gives rise to different bond cleavage and ring puckering channels. Furthermore, adding an aldehyde group (-C=O) onto furan, as a way to lengthen the delocalised ring electron system, opens up additional reaction channels via a nπ* state. The results presented here are used to build up a more complete picture of the dynamics that occur in small molecular systems after they are excited by a visible or UV photon, and are used as a basis to motivate further investigations. / <p>At the time of the doctoral defense, the following papers were unpublished and had a status as follows: Paper 5: Manuscript. Paper 6: Manuscript.</p>

The main topic of this project is the so called Edelstein effect. This recently discovered effect consists in the possibility of converting an electric field (a current) into a magnetization in materials that fulfill specific characteristics, more specifically materials where an effective Rashba spin-orbit coupling is present. The Edelstein effect is appealing to the scientific community from the fundamental physics point of view as well as from the technological point of view. In fact the possibility of efficiently converting an electric signal into a magnetic signal could revolutionize the current information storage technology. In this project, after a study of basic concepts of solid state physics: crystal structure, Bloch's theorem, spin-orbit coupling; we addressed the study of the basics of a powerful numerical tool, called density functional theory (DFT), for predicting the electronic properties of solids. This tool provides us with all the needed quantities for numerically calculating any kind of linear response, which we show that the Edelstein effect is a specific form of. Using a specific implementation of DFT, called augmented spherical wave (ASW), we calculate the Edelstein effect in iron and copper (where no effect is expected) and manganese silicide (where the effect is expected to appear). We also perform a systematic study on how the Edelstein effect depends on the symmetry of the material and the magnitude of the spin-orbit coupling. The calculations showed promising results from which we concluded that the numerical methods used could clearly distinguish between the presence of the Edelstein effect or not in mentioned materials.

Water is a fundamental part of life as we know it, and by that also a fundamental for biology, chemistry, and parts of physics. Understanding how water behaves and interacts is key in many fields of all these three branches of science. Numerical simulation using molecular dynamics can aid in building insight in the behavior and interactions of water. In this thesis molecular dynamics is used to simulate common rigid 3 point water models to see how well they replicate certain physical and chemical properties as functions of temperature. This is done with molecular dynamics program GROMACS which offers a complete set of tools to run simulations and analyze results. Everything has been automated to work with a python script and a file of input parameters. Most of the models follow the same trends and are valid within a limited temperature range. / Vatten är en av de fundamentala byggstenarna för liv, därmed är det även fundamentalt för biologi, kemi och delar av fysiken. Att förstå hur vatten beter sig och interagerar är en stor fråga inom dessa tre grenar av vetenskap. Med molekyldynamik går det att utföra numeriska simuleringar som kan användas som hjälpmedel för att bygga en djupare förståelse för riktigt vatten. I den här uppsatsen så har molekyldynamik använts till att simulera vanliga rigida 3 punkts parametiseringar av vatten för att se hur bra de kan replikera vissa egenskaper som funktioner av temperatur. Simuleringen är gjord med hjälp av molekyldynamik programet GROMACS som ger en fullständig uppsättning verktyg för att simulera och analysera molekylsystem. Alla simuleringar och analys är automatiserat med ett pythonprogram och en fil för parametrar. De allra flesta modeller följer liknande trender och är giltiga inom små temperaturintervall.