Advances in experimental physics, specifically light sources emitting at an attosecond time scale, has enabled the time resolution of atomic processes like photoionization. Recent developments have allowed these sources to produce light with non-linear polarization. There exists various theoretical methods that can simulate experimental set-ups that make use of these attosecond sources. The aim of this thesis project was to extend two of these methods to be able to simulate circularly polarized light in order to both better model experimental results and come up with new potentially interesting experiments. This has resulted in an extended version of the Random Phase Approximation with Exchange method capable of simulating an ionization process by light of arbitrary polarization, as well as well as an extended version of the NewStock package that is capable of time-resolved simulation of matter interactions with arbitrary light pulses.

I have investigated two different systems CO/Fe(100) and CO/Ru(0001), toobtain new information on the binding and desorption processes. The twodifferent systems have served as a model system, one for a static examination,CO on iron, and for the dynamic case, CO on ruthenium. To perform theseinvestigations, several types of techniques have been used such as, X-rayabsorption spectroscopy, X-ray emission spectroscopy, and femtosecond laserinduced desorption techniques such as two-pulse correlation. For the CO/Fe(100) system, we found that the on-top CO “<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Calpha" />1 phase” canbe described by the Blyholder-Nilsson-Pettersson model. The pre-dissociativephase of CO bound at hollow sites, “<img src="http://www.diva-portal.org/cgi-bin/mimetex.cgi?%5Calpha" />3 phase”, can be described in a Dewar-Chatt-Duncanson like picture. For the CO/Ru(0001) system, it was found that all our data could be fitted from an empirical friction heat bath model. Moreover, it turned out, thatthere is a strong frictional coupling to the substrate electrons and phonons.

Målet med det här projektet var att undersöka huruvida en XRF signalkan förbättras genom att filtrera denna genom en tunn skiva avantingen aluminium, bly eller molybden. För att undersöka dettaanvändes programmet MCNP6.2 för att simulera strålningsspektrat fråntvå olika strålkällor; ett röntgenrör av Wolfram som kan genererafotoner med energier så höga som 120keV, och ett radioaktivt Co-57preparat. Projektet visade på att detta är möjligt, och även attaluminium är att föredra i de flesta fall då det förbättrar XRFsignalenavsevärt, utan att behöva vara varken väldigt tjockt, elleroapplicerbart tunt. Utöver detta är aluminium även billigare samtlättare än de båda andra materialen. Även molybden kunde filtrerastrålningen på ett användbart vis när en Co-57 källa används. Dockbehövde filtret vara extremt tunt, därför rekommenderas ej molybden.Projektets slutsats var att ett 0,3 mm tjockt aluminiumfilterförbättrar signalen som mest när röntgenröret användes som källa,medans ett 0,8 mm tjockt aluminiumfilter fungerar bäst för Co-57 källan.

The ALPHA experiment at CERN is an ongoing project which tests fundamental symmetries between matter and antimatter by producing and trapping antihydrogen atoms in order to perform precision spectroscopic measurements. A logical next step is to form the antihydrogen molecular ion (consisting of one positron and two antiprotons). This system possesses net charge, and can therefore be trapped electrostatically, making repeated measurements possible. Moreover it has been suggested that the molecule has the potential to allow for higher-precision comparisons with ordinary matter than have been attained with the atom. Since both momentum and energy have to be conserved in a collision, a simple collision process between an antihydrogen atom (“Hbar”) and an antiproton (“pbar”) does not suffice in order to form the molecular ion. However it is possible, upon mixing of the two species, for a pbar colliding with an Hbar in the ground electronic state to form a metastable molecular state (i.e., a resonance) which is weakly coupled to a stable molecular state (i.e., a bound state) via spontaneous quadrupole transition. During the time a metastable ion exists, a second pbar can happen to undergo a Coulomb collision with the metastable molecular ion. The quadrupole electrostatic interaction with this secondary antiproton acts as a time-dependent perturbation on the molecular system which can strengthen the coupling between resonance and bound state. Hence a collision with a secondary pbar can induce a transition to a bound state whereby the excess energy is carried off by the secondary pbar. This work aims to determine the efficiency of the process just described. On the theoretical side, the following is done: a study is conducted on the topic of resonance scattering as it relates to the problem in consideration; building on this study a generalized time-dependent perturbation theory is constructed which is valid for transitions to and from resonant states as well as bound states. On the numerical side: the effective potential for pbar-Hbar scattering in the ground electronic state is obtained numerically within the adiabatic approximation; the energies and lifetimes of the resonant states of the molecular ion are estimated; a temperature-dependent rate coefficient is obtained for the process described which, in order to obtain a proper rate, needs to be multiplied by the square of the density of the antiproton plasma and by the number of antihydrogen atoms. It is concluded that at current capacity for trapping and storage of pbar and Hbar the process examined is not competitive with respect to other formation routes which have been proposed for the molecular ion.

One way of realizing a quantum computer is to use an ion trap. The research group Trapped Ion Quantum Technologies at Stockholm university were operating an ion trap with strontium ions. To increase the coherence time they installed a magnetic field shielding. Therefore the experimental setup had to be partially rebuilt. A new 405 nm laser was installed in order to speed up the ionization step of neutral strontium atoms. The characterization of the laser was performed and it showed that the laser could be operated at the required wavelength. The wavelength was characterized with respect to temperature and power. A scan of the 422 nm Doppler cooling laser was also performed and it showed that the Doppler cooling worked as intended. Lastly, Rabi oscillations were performed to see if coherent manipulation of the ion's quantum state worked as intended. This experiment was also successful but it showed some differences between having the magnetic shielding door open or closed which should be investigated further.

According to Bröstcancer förbundet, mammography is not efficient at detecting tumors in dense breast tissue or diagnosing breast cancer at its early stages. Ultrasound-optical tomography (UOT) is an imaging technique in development and has the potential for deep-tissue imaging. If ultrasound-optical tomography were implemented, it would be easier to differentiate between malignant, benign, and healthy tissue from any type of breast tissue. UOT is an imaging technique that takes advantage of high penetration depth and high spatial resolution of ultrasound imaging and optical imaging. In UOT, a laser light and an ultrasound pulse propagate through the tissue simultaneously at a frequency f$_L$ and f$_{US}$, respectively. The light will scatter while it propagates through the tissue and some of this scattered light will become frequency shifted by ultrasound pulse due to the acousto-optic effect. The tagged light will have the frequency $f_T = f_L + f_{US}$. The tagged (frequency shifted) light can be separated from the untagged light (unshifted light) using a thulium-doped lithium niobate, Tm$^{3+}$:$~$LiNbO$_3$, crystal as a filter. The crystal is kept at a temperature close to zero kelvin because then it exhibits unique characteristics, e.g. it has a narrow linewidth and long-lived hyperfine levels at this temperature. The filter is created by a method known as spectral hole burning (SHB). A laser beam is used to transfer electrons from the ground state to the excited state to create a hole at a specific wavelength. The spectral hole is created at the frequency of the tagged light and hence a narrow bandpass filter is constructed inside the crystal. The tagged light is fully transmitted through the filter while it highly attenuates untagged light. The tagged light is detected with a photodiode and processed in MATLAB after it has been transferred to an oscilloscope. This thesis aims to model and design a phantom probe that minimizes vibration and other unwanted movements or disturbances during measurements. The automated phantom holder will be used for the recording of 3D images. Another task of the thesis was to obtain the absorption spectrum of a 0.005$\%$ Tm$^{3+}$:$~$LiNbO$_3$ crystal when it is cooled down to 3$~$K to ensure that the crystal has the same absorption characteristics as predicted in literature. The absorption line at $\sim$ 800$~$nm is of interest since oxyhemoglobin and deoxyhemoglobin have similar absorption coefficients at $\sim$ 800$~$nm. Optical absorption and scattering information will help determine if the sample contains a cancerous region. The phantom probe was modeled in Solid Works and manufactured through 3D printing. In this setup, the sample holder was chosen to be translated while the ultrasound transducer was stationary to generate less blurry images. The design of the probe has to accommodate two detection schemes, reflection and transmission mode. The phantom probe was automated using a linear servo actuator since it was controlled with pulse-width modulation (PWM). It used a square signal as an input that could be generated with an Arbitrary signal generator (AWG). Using a device that operates with a signal was important because it would make it easier to integrate it into the experimental setup. The whole phantom probe was constructed in a cost-efficient way and in a way that it could be easily incorporated into the experimental setup. The absorption spectrum showed that the crystal has an absorption line at $\sim$ 794.3$~$nm. This absorption spectrum was compared to an absorption spectrum taken at 8$~$K on the same crystal and captured with a different method. Both absorption spectra had the same absorption peaks at almost the same wavelengths but they also showed few discrepancies that may depend on the temperature difference and the recording method. In this thesis, the absorption spectrum data taken was captured by sweeping the wavelength. The signal was captured with a photodiode, transferred to an oscilloscope, and then processed in MATLAB. The absorption spectrum data at 8$~$K was obtained using a Fourier transform spectrometer, resulting in data with little noise and well resolved peaks. To conclude, a functional and robust phantom probe was designed and manufactured that could withstand vibration and other undesired movements. An absorption spectrum of Tm$^{3+}$:$~$LiNbO$_3$ crystal was obtained at 3$~$K and compared to absorption taken at 8$~$K and compared to literature and previous measurements under similar conditions.

Plasmonic effects in nanosized particles enhance the interaction between light and matter due to the localized surface plasmon resonance, with potential applications such as all-optical transistors and optical computers. Commonly, the dynamics of nanoparticles’ optical properties are assessed via pump-probe spectroscopy, where a plasmonic structure is exited by an initial laser, the pump. Thereafter a second, less intense laser, a probe, interacts with the now excited structure at a time delay. Through measurements of the probelight transmitted by the matter, the optical dynamics of the structure are monitored. Similar methodologies can potentially be used for other applications as well, such as all-optical switching. This study focuses on an implementation of a numerical finite element method model simulating a pump-probe experiment to predict the effects of different geometries and evaluate experimental data. The simulations are split into three parts. Initially, periodically spaced nanoparticles are excited by the pump laser. Then the model estimates the internal thermal dynamics of the excited nanoparticles and in turn, determines the change in complex permittivity. Lastly, the probe-matter interaction is modeled. To evaluate the model, a comparison with another model was performed. Furthermore, simulations of periodically spaced gold dimer nanoparticles in air were done to investigate how dimers affect transmitted light. For a probe light polarization rotated 45◦ against the axis parallel to the dimer, a change in rotation of 6◦ over 35 fs was induced by the pump, indicating a potential switching mechanism.

This licentiate thesis concerns topics in non-interacting and interacting quantum physics in one dimension. We present the notions of Wannier functions and tight-binding models. Quantum walks are discussed, quantum mechanical analogues to random walks. We demonstrate the ideas of Bloch oscillation and super-Bloch oscillation - revivals of quantum states for particles in a periodic lattice subject to a constant force. Next, the Rabi model of light-matter interaction is derived. The concept of quantum phase transitions is presented for the Dicke model of superradiance. The idea of adiabatic elimination is used to highlight the connectedness of the Dicke model. Finally, we present a one-dimensional interacting system of resonators and artificial atoms that could be built as a superconducting circuit. Using adiabatic elimination as well as matrix product states, we find the phase diagram of this model.

The aim of this study is to study the ground-state of various elements including Hydrogen molecules and Heliumatoms using a self written Density Functional Theory code. We limit ourselves to simple linear moleculesusing cylindrical symmetry, for which the computational difficulty is manageable and appropriate for anundergraduate thesis. We focus on the binding length and energy of the molecules stated here. Charge densityis calculated using the Poisson equation, which is used to calculate the potential and correlation potential. From the distance dependent of the total energy, the chemical bond length can be determined. The results showa total energy for a Hydrogen molecule is -31.3 eV and most optimal binding length is identified at 0.76 Å.

The present master's thesis deals with numerical modeling of solid-state micrometrical-sized polymeric dye lasers, commonly denoted as microcavities. It is part of a large research initiative carried out in the optics group, at the MAP (Microelectronics and Applied Physics) department in KTH (Kungliga Tekniska Högskolan - Royal Technical School) and targeted towards the design and manufacturing of micro- and nano-scaled polymeric components for nano-photonics, primarily lasers. The finite element method (FEM) in frequency domain is used as a primary modeling tool through the simulation software COMSOL Multiphysics. Models for spontaneous emission, optical losses and gain are developed and demonstrated. A specic layout is studied: the double hexagonal microcavity. While it was expected to be a good candidate for a laser, the design shows unexpected properties making it useful for sensing applications. Finally, the transposition of models to time domain is initiated : a replacement solution for the lacking perfectly matched layer (PML) in Comsol is developed and demonstrated. Methods for modeling materials parameters in time domain are investigated, together with the possible use of a more suitable algorithm : finite dierences in time domain (FDTD) or Yee's scheme.