The field of terahertz time-domain spectroscopy (THz-TDS) is still far from reaching its full potential, but is a very promising utility for a wide range of applications. Principle experiments have been performed in fields of drug screening, pharmaceutical, medical diagnostics, security imaging and detection of explosives. Optimized and adapted THz-TDS systems holds great promise for driving this technology further.The purpose of this thesis was to build a THz-TDS system, explore possibilities for improving this system and to perform THz-TDS measurements on semiconductors and wood. The aim of the experimental work was to build a stable and reliable system with an electric field strength of THz radiation in the order of kV/cm. The THz-TDS system used in this thesis was based upon the principles of optical rectification and free-space electro-optic sampling in zinc telluride (ZnTe) crystals using a femtosecond Ti:Sapphire amplified laser.Theoretical studies were performed on the principles of generation and detection of THz radiation. The experimental work was based on publications of similar experiments. Theoretical and experimental studies lead to several modifications and improvements of the setup first built in this thesis. Experiments were performed on disparate materials to find suitable materials for THz transmission. Results from measurements performed on semiconductors and wood, obtained by THz-TDS, were analysed to find the absorption coefficient and the refractive index of the materials. The spectroscopic information obtained by THz-TDS can also be used to find the conductivity and the mobility of these materials. THz-TDS measures the electric field and therefore provides information of both the amplitude and the phase of the THz wave. A Fourier transformation was used to obtain the frequency spectrum of the detected signal. The improvements were done by analysing the results of the detected signal to see which adjustments and modifications to the setup that had positive effects on the results. The pump power used for generation of THz radiation and the optimum azimuthal angle of the ZnTe crystals were crucial to obtain a THz-TDS system with a strong electric field. The maximum electric field strength for the THz radiation in this thesis was 13.2 kV/cm, with a signal-to-noise ratio of 43 and dynamic range of 1500.

In this report, a novel method for making single strings of particles is presented.These strings were characterized using diverse electromechanical methods

The main goal of this thesis is to establish a method and estimate the complex materialconstants for the radial and thickness mode. This has been done in two separate methods. For the thickness mode material constants, a optimization script in MATLAB has been developed, which is capable of directly optimizing all the input parameters for the xTrans, for both active and passive layers. The method has been evaluated, and the complex material constants describe behavior in accordance with measured data. For estimating the radial mode complex material constants, an evaluation a publish method by S.Sherrit has been done.

This Master's thesis is a continuation of the specialization project I did during the spring of 2011. The goal of said project was to set up a system for UV-photoluminescence experiments in the Nanophotonics laboratory at the Department of Electronics and Telecommunications at NTNU, and conduct photoluminescence spectroscopy measurements on different zinc oxide nanostructures, including GaAs/AlGaAs/ZnO core/multishell nanowires. This thesis involves studying zinc oxide nanowires using both a continuous wave and pulsed ultraviolet laser light, and the final goal is to optically excite these nanowires so they achieve lasing. Using a Tsunami Ti:sapph mode-locked tunable laser and a flexible harmonic generator, laser pulses with a pulse duration of 2 ps could be generated at wavelengths around 300 nm, at a power of around 5 mW. At this power, some of the wires showed possible signs of optical gain, but since it was not possible to apply more power to the wires, this could not be confirmed. If there had be enough time, both low temperature measurements and time-resolved spectroscopy, using a streak camera, would have been performed.

The optimization of piezoelectric ultrasonic transducers has tradisionally been done through trial and error, somewhat guided by one-dimentional simulations. This can often be a very time-consuming and expensive process, hence a more extensive simulation method is desired.A series of finite element models of piezoelectric ultrasonic transducer has been made in COMSOL Multiphysics. The initial models were designed to emulate the conditions assumed in a one-dimentional transducer model, and their validity could thus be confirmed by said model. Later models did not emulate these conditions, and a lossless model of a spherical disc with backing and a single matching layer was successfully implemented. Attemps had been made to include mechanical loss in the initial models, but was only partially achieved. All loss was thus excluded from later models. A final model with a piezoelectric layer poled in the radial direction was not successfully designed, as the varying poling direction proved to be difficult to implement.