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In this bachelor’s thesis, a fabrication process for channel waveguides in LiNbO 3crystals using the proton exchange technique is developed and characterized. These waveguides can be used at the laser physics department at the Royal Institution of Technology, KTH, for specifically non-linear optical applications. A waveguide is a device that guides a wave. In this case an optical waveguide is fabricated and so it guides electromagnetic waves in the optical spectrum that is light. To guide the wave diffraction has to be prevented in one or two dimensions, constraining the light to travel along a certain desired path. Waveguides can be fabricated in small sizes down to the micrometer level. The small structures can yield high-intensity guided waves with low input powers and this can lead to more efficient and compact nonlinear devices (sensitive to the field intensities). This makes it possible to produce compact and efficient devices with waveguides. To confine the light in the waveguide, the refractive index at the surface of the crystal will be increased creating a guiding layer in that region. The index increase is achieved by proton exchange. Proton exchange is a process where the lithium ions at the surface of the crystal are exchanged with hydrogen ions. This exchanged part makes the guiding layer because the hydrogen ions increase the refractive index of LiNbO 3. The fabrication process of the channel waveguides consisted of transferring a mask pattern into the LiNbO 3crystal. To do this, titanium was uniformly deposited on the crystal and on top of it a layer of photoresist was spun. The mask was transferred into the photoresist by photolithography and then etched into the titanium. The proton exchange could then take place in the mask openings. The progression of the fabrication was carefully documented after each step of the process to assess the quality of the waveguides. Several waveguides were fabricated on each sample with widths ranging from 2 to 10 microns. In the end, the full process for waveguide patterning and fabrication was developed on LiNbO 3 substrates. The fabrication recipe developed in this work allowed for reliable fabrication of uniform channel waveguides over the whole sample length, L=12 mm, with widths down to 1.02 μm. A remarkably good result if one considers that this is beyond typical resolutions (~2μm) of the lithographic system used in this work.

The basic idea of non-contact Atomic Force Microscopy (AFM) is to generate an image of a surface by scanning with a sharp probe on a sample, without touching. During the scan the reactions due to the non-contact forces between the tip of the probe and the surface are measured. There is interest in imaging biological samples with AFM, but conventional AFM cantilevers perform poorly in a liquid environment, which is required for many measurements in biology. The aim of this report is to find out if a crystal bulk mode resonator can be used as an alternative to a conventional cantilever in liquid. AFM measurements are limited by noise. To get sensitive measurements the noise needs to be minimized. However, the noise originates from random thermal motions, which will always be present at non-zero temperatures. The noise determines the fundamental limit of sensitivity for a certain resonator. Therefore we study the thermal noise from a crystal resonator when operating in a liquid environment. This is done by building a circuit that amplifies the noise signal from the resonator. / Idén bakom Atomic Force Microscopy (AFM) är att generera en bild av en yta genom att svepa en skarp prob över den utan kontakt. Medan man sveper över ytan mäter man reaktionskrafterna på proben från ytan. AFM-mätmetoder är intressanta för biologiska ändamål, men konventionella AFM-probar fungerar inte särskilt bra nedsänkta i vätska, vilket är en förutsättning för många mätningar inom biologin. Målet med denna rapport är att ta reda på ifall en longitudinellt oscillerande kvartskristallresonator kan användas som alternativ till en vanlig AFM-prob för mätningar i vätskemiljö. AFM mätningar begränsas av brus. För att få en känslig mätning måste bruset minimeras. Bruset härrör dock till större del från slumpmässig termisk rörelse kring oscillatorn, vilket inte kan elimineras. Detta brus bestämmer den fundamentala precisionsgränsen för en viss resonator. Därför kommer vi, i denna rapport, att studera bruset från en kristallresonator i vätskemiljö. Detta görs genom att bygga en elektrisk förstärkarkrets för att förstärka brussignalen från resonatorn.

Mode-locked lasers are used for a vast amount of applications, e.g. corneal surgery[1] and optical data storage[2] . The currently established technique for mode-locking with a semiconductor saturable absorber mirror is expensive and in- volves a fairly advanced production technique[3] . Carbon nanotubes incorporated into thin plastic films present an easy to produce and comparatively cheap alter- native. These films are produced by solving carbon nanotubes in a proper solvent, mixing with a host plastic material and finally spin coating to a substrate. Earlier studies have successfully produced and used carbon nanotube thin film saturable absorbers for mode-locking, most notably in the near infrared spectral region[4] . In this work, different solutions are produced using different solvents and varying the carbon nanotube and plastic ratios in these solutions. The different solvents used were toluene, 1,2-dichlorobenzene and acetone. Another fabrication parameter is the revolutions per minute used during the spin-coating process. and the revolutions per minute varied between 500-1250. A total of 17 different solutions was prepared, and spin-coated onto glass substrates with different revolutions per minute. Although proper mode-locking could not be achieved for most of the samples the best solvent seemed to be 1,2-dichlorobenzene which is used in other studies as well[5, 6] . As a result of the laser’s output, which shows modulation, a conclusion of that the sample has non-linear absorber properties can be made. A tendency for q-switching was also observed, however, this operation is unstable in terms of repeti- tion rate. To be able to get desired laser behavior the modulation introduced by the absorber has to be adjusted, by altering e.g., the film’s thickness or carbon nanotube concentration. No proper mode-locking was observed for toluene regardless of the concentration of solvent or carbon nanotubes.

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The Higgs to Two Photon decay channel is analyzed to one-loop in the Feynman gauge.  Triangle loop processes are evaluated using dimensional regularization due to divergent integrals.  The build up to Higgs physics is given by way of gauge theories in the Standard Model where we can then introduce the Higgs field.  After evaluation of the Higgs di-photon channel, we explore questions of non-perturbative approaches to these calculations, higher order precision calculations, and probing ideas beyong the Standard Model.