The discoveries and subsequent developments within the field of metamaterials have opened up for novel light-matter interactions towards the engineering of light behavior. The astonishing phenomenon of negative refraction remains challenging to realize for visible frequencies, and non-magnetic gain metamaterials have been proposed towards this end. This thesis pursues this idea by presenting a conceptual framework for which to understand the requirements and possibilities emerging from the causal behavior of the dielectric response. This results in clear and concrete instructions on how the dielectric response must be designed towards negative refraction. These are offered in terms of a novel perspective employing zero- and pole placements in rational functions and analysis of the dielectric function in its complex plane. A number of negative index systems are evaluated including two component media and low gain negative index media. Negative index concepts are introduced to the Electromagnetically Induced Transparency system. A strategy towards design and realization of arbitrary dielectric responses in terms of Krein and Nudel'man causal extrapolation is also presented.

Ultrafast pump-probe spectroscopy is a powerful technique for measuring decay times for an optically excited system, e.g. a semiconductor, on the pico- to femtosecond time scale. We present both a classical approach and a quantum mechanical density matrix approach to simulate the pump-probe signal and compare the two. The main features of a typical pump-probe experiment are explained and the "coherent artifact" is accounted for. With a three-level density matrix approach we explain some experimental features from pump-probe studies of gallium arsenide (GaAs). A simple model for simulating pump-probe of semiconductors is introduced, and the relation to the density matrix approach is derived. We also show how the semiconductor model reproduces the main features of experimental data from pump-probe studies of GaAs.

The effect of optical coatings on the longitudinal magneto-optic Kerr effect response from 10 nm thin films of permalloy (Ni84Fe16) has been studied. Enhancement of the magneto-optic Kerr effect signal contrast of a factor 1.76 has been observed for P- polarized incident light on a trilayer configuration of aluminium, magnesium fluoride, and permalloy. A quadrilayer structure where the trilayer is overcoated with zinc sulphide enhances the signal contrast by a factor 4.05 for P-polarized light. The enhancement is also observed for S-polarized light, and is shown to be reproducible using nickel as the magnetic material and gold instead of aluminium.The experimental data are compared to a simplified theoretical model where the electric field components are calculated using a 4 x 4 matrix algorithm. The model is found to be inadequate in predicting the longitudinal magneto-optic Kerr effect response from complex multilayer structures. This is believed to be due to a simplification in the model disregarding the phase factors of the different components reflected off the multilayered samples.

The differential scattering cross section for diffuse scattering of X-rays from thinfilm structures is discussed within the framework of the distorted wave Born ap-proximation (DWBA). In contrast to the standard Born approximation (BA), thedistorted wave approach succeeds in calculating scattering from surfaces near thecritical angle of reflection. The method is particularly useful for studying averagesurface properties.Compromises made in the derivation of the model substantially simplify thefinal expression, but also limit its range of validity, which depends on the surfaceroot mean square roughness &#963; and the momentum transfer between the incidentand scattered X-rays perpendicular to the surface, Qz . The approximation is validso long as (Qz x &#963;) << 1.However, this is also the only regime where it is necessary togo beyond the simpler Born approximation.A computer simulation software based on the DWBA is implemented in Python.The implemented DWBA depends on the fractal dimension of the surface featuresthrough a parameter h (D = 3 &#8722; h) and an in-plane correlation cut off length &#950;.The various effects of changing key model parameters, among them &#950; and h, isdemonstrated. Comparison between experimental data and the DWBA modellooks promising although there are some challenges in relation to determiningthe fractal dimension.Finally, the feasibility of implementing the DWBA model in a multi-parameterfitting algorithm is discussed.

In nanoparticle research it is common to perform optical measurements on particle films during deposition, to help understand the growth process. GranFilm is a software under development which can calculate the optical properties of an array of truncated nanoparticles supported on a substrate. The theory behind these calculations is based on the work of Bedeaux and Vlieger. One feature which was missing from the software until now was the ability to do such simulations on the case of truncated spheroidal nanoparticles with an arbitrary number of coatings of different materials. In the beginning of this work, the equations needed to perform these simulations are derived, and then reduced to previously derived special cases for verification. The new equations are then implemented into GranFilm, and the new code is put through numerical tests. Finally, the new functionality is tested with the help of experimental data from an oxidation process of a silver nanoparticle film. The qualitative evolution of the optical properties of the film is reproduced quite successfully, but some issues remain.

With the prospect of producing superhydrophobic and mechanically stable biomimetic surfaces, the water repellent properties of springtail cuticles are investigated quantitatively. The analysis is based on apparent contact angle measurements on nine springtail species and SEM and AFM images of their cuticles. It is argued that water exists in a metastable Cassie-Baxter state on the cuticle and that three-phase line tension of the order of 10^-8 J/m contributes to high apparent contact angles. A model is developed to assess the significance of a recently reported re-entrant geometry of the cuticle granules and to study the resistance of the cuticle against wetting. The model estimates that springtails resist wetting under hydrostatic pressures up to 10^4 - 10^5 Pa, and that re-entrant granule profiles increase the wetting resistance by 50 - 400%. To explain the low contact angle hysteresis observed on the cuticles, new equations are proposed to include the effect of three-phase line tension. Again, a line tension magnitude of the order of 10^-8 J/m can account for the experimental findings. This work indicates that the sub-micron size scale of the springtail cuticle granules provides an elegant approach for achieving water repellent and mechanically stable surfaces. Two springtail species are singled out as especially promising for biomimetic applications.

In the present study, a process for fabricating GaAs nanowire/graphene hybrid devices using electron beam lithography processing techniques is presented and demonstrated. Fabricated devices were investigated electronically by measuring emph{I-V} characteristics under a variable gate voltage.Fabrication processes for both exfoliated and CVD-grown graphene were developed. For exfoliated graphene the outlined process is unsuccessful, as the graphene flakes were found to crumble and fall off during the first processing step following transfer. It is thus concluded that exfoliated graphene flakes are too delicate to perform any significant processing after graphene transfer.The fabrication process was successfully demonstrated in fabrication of devices with CVD-grown graphene. However, nanowires in these devices were seen to undergo significant corrosion during the process, which is credited to the water exposure associated with graphene transfer. This was found to be an especially prominent issue for contacted nanowires, where the metal contact is believed to facilitate galvanic corrosion. I-V characteristics and gate voltage dependence were measured for GaAs nanowire/graphene hybrid devices made with CVD-grown graphene. Large variations in the I-V behavior and gate voltage dependence was observed. This is credited to corrosion in the nanowires, which is thought to result in uncharacteristic behavior for metal-GaAs contacts. There are also indications that several devices are shortened by graphene. The electronic investigations are therefore found to be inconclusive in respect to the electronic properties of the graphene/GaAs nanowire junction. It is concluded that further developments in the fabrication process are needed to achieve GaAs nanowire/graphene hybrid devices suitable for detailed analysis.

<p>Sun exposure and climate therapy is an effective treatment for psoriasis. However, even though this treatment gives the patients relief from their discomforting symptoms, it has some potentially dangerous side effects such as an increased risk of skin cancer and premature skin aging. A prospective field study plans to follow the patients undergoing the climate therapy. During this study the UV dose to each patient will be monitored by personal dosimeters worn by the patients. Furthermore the patients' skin spectra acquired by the means of optical spectroscopy will be obtained daily. Both psoriatic skin a unaffected skin will be observed. These data will be used to assess the skin changes which take place during the psoriasis treatment. This project is focused on developing an automatic algorithm for handling bulk spectrometric measurements data and to propose ways of numerically evaluating the skin spectra. These numerical values will be later used to compare the daily patients' spectra and monitor progress of the treatment. An inverse model based on a lookup table and successive iteration was proposed in this project. The model matches the diffuse skin reflectance spectra modeled with a diffuse skin model with the measured patients skin spectra. The measured skin spectra are then defined by the diffuse skin model input parameters which were found by the inverse model. These parameters are oxygenation, blood volume and melanin absorption coefficient. Additionally four indexes were proposed to supplement the parameters found by the inverse model, namely the erythema index, melanin index, hemoglobin index and oxygenation index. Measurements of several skin spectra including psoriatic plaques spectra were carried out and used to test the inverse fitting model performance. The proposed model proved to match the measured spectra in an acceptable form employable for distinguishing between different measured spectra. The highest deviation is at the ends of the spectra due to the use of a constant value of scattering coefficient and additional parameters not directly relevant to sun exposure, hence not considered by the model. The proposed parameters together with the indexes proved to be a viable means of evaluating the healing in the psoriatic plaques as well as determining the changes caused by the sun in normal skin.</p>

<p>Speckle arises when coherent light is reflected from a rough screen and observed by an intensity detector with a finite aperture. Because speckle causes serious image degradation when lasers are used as light sources in e.g. projectors, methods for reducing the speckle contrast need to be developed. Different speckle contrast reduction methods are investigated in this thesis, such as a rotating diffuser and a sinusoidal rotating grating. In addition, speckle simulations with the optical system design software ZEMAX has been explored. A setup consisting of a 4-f imaging system with a rotating diffuser in the Fourier plane was developed in order to decide whether or not it is advantageous to perform speckle reduction in the Fourier plane. Hence, measurement series were performed with the rotating diffuser placed at different positions in the 4-f imaging system for comparison. Measurement series were executed both with an empty object plane and with a lens in it to spread the light in the Fourier plane. Placing a rotating diffuser in the Fourier plane does not appear to be effective for speckle contrast reduction. The last setup investigated was a transmissive spatial light modulator (SLM) placed in the beam path. Sinusoidal rotating gratings created by means of gray levels, to simulate a potential modulator based on a deformable polymer layer, were implemented on the SLM. The gratings were rotated around their centers, and in a spiral in order to reduce the speckle contrast. For the first method the modulator speckle contrast was 34% for N = 18 averaged images, and for the second method it was 31% for N = 36 averaged images, both with a grating period of 4 pixels. Due to the drawbacks of the SLM optimal results were not achieved, but the SLM is useful for a proof-of-concept. Further measurements should be performed for this promising, novel method based on a true sinusoidal grating.</p>

<p>A research group at the Norwegian University of Science and Technology plan to integrate Capacitive Micromachined Ultrasonic Transducers (CMUTs) in a probe which can be used to image human blood vessels from the inside. With CMUT technology still being in its youth, it is important to characterize different CMUT prototypes to learn which design is best suited for the probe. In this thesis, a network analyzer and a heterodyne interferometer are used to characterize two prototypes, both electrically and optically. The heterodyne interferometer was proven to be extremely sensitive and thus a valuable tool when investigating the behaviour of single CMUT cells. Measurements revealed that the cells within both the CMUT arrays had different resonance frequencies. This effectively broadens the band widths of the prototypes, but reduces their maximum acoustical output power, given that all the cells operate at the same frequency. It was found probable that the CMUT characteristics were influenced by how charges moved within the prototypes. These charging effects are quite complex and would in practice make it hard to predict where the centre frequency of the CMUT array lies from time to time. The vibration pattern of most the cells at their respective resonance frequencies looked healthy both in air and immersed in a liquid when measuring with the interferometer. Immersed, the resonant frequency range of the CMUT become wider, but the peak was located at a lower frequency than in air. The next CMUT prototype to be tested in the future does not fit into the experimental setup. A plan to adapt the setup has been presented in this thesis, making it more practical to handle different samples. This design would also make it easier to investigate crosstalk effects between neighbouring CMUT elements within the arrays. Knowledge aquired in this thesis will hopefully help researchers figure out which areas of the CMUT design have the potential to be improved.</p>