Liquids and molecular solids investigated by THz time-domain reflection and parallel-plate waveguide spectroscopy

Abstract

In this thesis, two THz-TDS systems were presented. The first one was the reflection THz-TDS system for the study of liquids. By using this system we measured liquid water as well as water based HCl and NaCl solutions. The Debye model and an extend model based on the Debye model and harmonic dampened oscillators were used to analyze the measurement results of liquid water and water based solutions. The second one was a compact low-temperature parallel metal-plate waveguide THz-TDS system. Using this system we studied the temperature dependence of newly developed photo-Dember emitter as well as the temperature dependence of an absorption line of 1, 2-dicyanobenzene below 1 THz.In Chapter 2, the experimental basics were described. THz time domain spectroscopy using ultra short laser pulses was reviewed. THz generation from a large area microstructured photoconductive switch and from a photo-Dember emitter as well as THz detection using an electro-optic crystal were carefully introduced. The principle and setup of the time-domain technique used in this work (ASOPS) was described. The fundamentals of interaction between electromagnetic waves and matter were also given in this chapter.In Chapter 3, we presented THz time domain reflection spectroscopy of aqueous systems. The data analysis required for data obtained in this setup was also given. The Debye model and dampened harmonic oscillator model were carefully introduced and applied for the analysis of the dielectric relaxation of water and water based solutions. A linear increase of the dielectric function compared with pure water with increasing ion concentrations was verified by both experiment and theoretic analysis.In Chapter 4, we presented a compact low-temperature THz parallel plate waveguide spectrometer. The temperature dependence of the system including the photo-Dember emitter, the copper plate, and the electro-optic crystal was discussed. Using this setup we measured the absorption of 1,2-dicyanobenzene at different temperatures. We found that the absorption peak around 750 GHz of 1, 2-dicyanobenzene displays a blue shift with increasing temperature.