The objective of this thesis has been to investigate novel host material configurations for high-power end-pumped Er-Yb co-doped, or Yb doped microchip lasers and try to increase their performance. In Er-Yb co-doped systems, the main limitation is the thermal shortcomings of the phosphate glass host material. The thesis presents some novel results that contribute to the search for a crystalline replacement. In Yb doped systems, most end-pumped schemes reported have been using relatively low-power single-emitter diodes. The thesis presents experiments with Yb:KGW microchips end-pumped by high-power diode bars. Another common limitation of end-pumped Yb microchip lasers is the thermal lens that destabilizes the cavity and decreases the beam quality. The approach to reduce the thermal lens by using an athermal propagation direction has been evaluated and the results are presented in the thesis. In the search for a crystalline host material for Er-Yb systems, borates have been found increasingly interesting. Consequently, we started out by investigating Gadolinium-calcium-oxoborate, GdCOB, which could be grown in platinum crucibles. It was found that the cw performance of such monolithic microchips is quite comparable to glass hosts in terms of slope efficiency, but the threshold is significantly larger. As for Q-switched performance, which is essential to most Er-Yb applications, the first efficient Q-switched results with a crystalline host is presented in the thesis. Similar to the cw regime, the slope efficiencies are comparable to glass, while the threshold is quite high. However, the perhaps most important parameter, maximum output power before thermal fracture, is neither significantly improved nor worsened compared with phosphate glass. This is believed to be due to higher threshold and a stronger thermal expansion that negates the benefit of a thermal conductivity that is only 2-3 times higher. To find a host material that could withstand higher pump powers, we turned our attention to the double-tungstates KGW and KYW, which have higher thermal conductivity and higher cross-sections. They have, however, energy level lifetimes which differ significantly from glass or borates and as a consequence, a thorough spectroscopic investigation has been undertaken to optimize dopant concentrations. Laser experiments on crystals with dopant concentrations based on this investigation are expected in the near future. When pumping Yb:KGW with a high-power diode bar, we achieved output powers of 9 – 12.4 W under different experimental conditions with incident powers of 18.3 – 26 W. The incident power of 26 W in one design was enough to fracture the crystal. Using a crystal cut for propagation along an athermal direction and comparing it with an identical b-cut crystal, we found that the thermal lens in the athermally oriented crystal was about a factor two weaker at the same absorbed power. / QC 20101116

Measurements of film mass flow rate for annular, diabatic steam-water flow in tubes are presented. The measurements were carried out with four axial power distributions and at several axial positions at conditions typical for boiling water reactors, i.e. 7 MPa pressure and total mass flux in a range from 750 to 1750 kg/m2s. The results show that the influence of the axial power distribution on the dryout power corresponds to a consistent tendency in the film flow rate and that the film tends to zero when dryout is approached. Furthermore it is demonstrated that two selected phenomenological models of annular flow well predict the present data. A model for additional entrainment due to boiling is shown to degrade the predictions. / QC 20101108

We studied the mutual neutralization of Li+ and H- at effective collision energies of a few hundred meV, which corresponds to temperatures of around 2000 K, in the double ion storage ring DESIREE.We present a new approach to match beam velocities and a new general analysis method for non-fragmenting mutual neutralization at DESIREE.Our results show two features, which we could clearly assign to the product channel into the electronically   excited  3s state of neutral lithium and an unresolved combination of 3p and 3d final state contributions.Branching fractions into 3s are extracted for ten different collision energies via spectral binning and compared to several theoretical investigations and two previous measurements, which focused on the heavier isotope deuterium.We find a significant isotope effect, as theoretically predicted, but in contrast to previous experimental results. The branching fractions agree well with different theoretical approaches using non-empirical couplings and  best with a combination of ab initio potentials and Landau-Zener transition probabilities.

Microphotonics has been offering a body of ideas to prospective applicationsin optics. Among those, the concept of photonic integrated circuits (PIC’s) has recently spurred a substantial excitement into the scientific community. Relisation of the PIC’s becomes feasible as the size shrinkage of the optical elements is accomplished. The elements based on photonic crystals (PCs) represent promising candidacy for manufacture of PIC’s. This thesis is devoted to tailoring of optical properties and advanced modelling of two types of photonic crystals: (Bi3Fe5O12/Sm3Ga5O12)m and (TiO2/Er2O3)m potentially applicable in the role optical isolators and optical amplifiers, respectively. Deposition conditions of titanium dioxide were first investigated to maximise refractive index and minimise absorption as well as surface roughness of titania films. It was done employing three routines: deposition at elevated substrate temperatures, regular annealing in thermodynamically equilibrium conditions and rapid thermal annealing (RTA). RTA at 500 oC was shown to provide the best optical performance giving a refractive index of 2.53, an absorption coefficient of 404 cm−1 and a root-mean-square surface roughness of 0.6 nm. Advanced modelling of transmittance and Faraday rotation for the PCs (Bi3Fe5O12/Sm3Ga5O12)5 and (TiO2/Er2O3)6 was done using the 4 × 4 matrix formalism of Višňovský. The simulations for the constituent materials in the forms of single films were performed using the Swanepoel and Višňovský formulae. This enabled generation of the dispersion relations for diagonal and off-diagonal elements of the permittivity tensors relating to the materials. These dispersion relations were utilised to produce dispersion relations for complex refractive indices of the materials. Integration of the complex refractive indices into the 4 × 4 matrix formalism allowed computation of transmittance and Faraday rotation of the PCs. The simulation results were found to be in a good agreement with the experimental ones proving such a simulation approach is an excellent means of engineering PCs.

To understand the function of macromolecules like proteins it helps to know the structure of the molecule. Coherent diffraction imaging is an emerging method that might be used to figure out the structures of macromolecules. In this method diffraction patterns of the macromolecule are recorded by shining light on the molecule from many unknown orientations and detecting the pattern of the diffracted photons. By assembling the diffraction patterns in a specific way and finding the phase of the photons that gave rise to the diffraction patterns, it is theoretically possible to obtain the electronstructure of the molecule and thus the molecular structure. The assembling of several thousand diffraction patterns representing unknown orientations of the molecule is hard to do by hand, but there are several methods that can be used. The EMC (Expand-Maximize-Compress) algorithm is one of those methods. It is an iterative algorithm that tries to create a model describing the Fourier Transform of the electron density of the molecule by maximizing each diffraction patterns fit to the model. This work examines how sensitive the EMC algorithm is to datasets with few diffraction patterns or a low intensity of the light being diffracted by the molecule, for the proteins phytochrome and lysozyme. The result of the work could be used to make sure enough data in collected in real experiments. Diffraction patterns simulated with the program Condor is used in this work, instead of diffraction patterns from real experiments.EMC finds the correct model when the data set contains about 1/3 fewer photons for the smaller more symmetrical molecule lysozyme than it does for phytochrome. This might be because the shapes in lysozymes diffraction patterns are larger than in phyochrome’s patterns. For phytochrome the EMC algorithm assembled the diffraction patterns correctly, with fewest photons for the light intensity 0.764 J/μm2 and 1250 diffraction patterns. For lysozyme it was with an intensity 1.910 J/μm2 and 1425 diffraction patterns. More investigation of the data is needed to understand what factors that affect the EMC algorithms ability to assemble the diffraction patterns correctly. / För att förstå makromolekylers kemiska eller biologiska funktion so underlättar det om man känner till molekylens kemiska struktur. Med den nya tekniken “coherent diffraction imaging” ska det vara möjligt att lista ut makromolekylers struktur. I denna teknik detekterar man diffraktionsmönster av molekylen genom att belysa molekylen med ljus från många olika okända vinklar and registrera mönstret som skapas av det diffrakterade ljuset. Genom att sätta ihop alla dessa diffraktionsmönster på rätt sätt och sen återskapa fasen för ljuset i diffraktionsmönstret så kan man generera molekylens elektronstruktur och från elektronstrukturen kan man få tag i molekylens struktur. Att sätta ihop tio tusentals diffraktionsmönster med okända vinklar på rätt sätt är väldigt svårt att göra, men det finns flera olika metoder som kan användas. EMC (Expand-Maximize-Compress) är en sådan metod. EMC är en iterativ algoritm som skapar en modell av (Fourier transformen av) molekylens elektronstruktur genom att maximera hur bra diffraktionsmönstren passar med modellen. Detta arbete utreder hur bra EMC algoritmen är på att hitta rätt (Fourier transform av) elektronstruktur när väldigt få diffraktionsmönster används eller när intensiteten på ljuset som sprids av molekylen är lågt. Programmet Condor används för att generera teoretiska diffraktionsmönster för de 2 molekylerna lysozym och fytokrom. EMC används sedan med olika uppsättningar av intensitet och antal diffraktionsmönster för att skapa en modell av elektronstrukturen. EMC behövde ca 1/3 färre antal fotoner i sin modell för att hittar den rätta modellen av elektronstrukturen för den lilla symmetriskt formade molekylen lysozym än för fytokrom. Att det är lättare för EMC algoritmen att hitta den korrekta modellen för lysozym än fytokrom kan bero på att lysozyms diffraktionsmönster har större former/features eller på lysozyms storlek och form. EMC körningen som behövde minst antal fotoner för att hitta den korrekta elektronstrukturen för fytokrom hade intensiteten 0,764 J/μm2 på det inkommande ljuset och behövde 1250 diffraktionsmönster. För lysozym behövdes det 1,910 J/μm2 och 1425 diffraktionsmönster för att EMC algoritmen skulle hitta rätt modell av elektronstrukturen.

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.