Single cycle terahertz pulse propagation in water

Single cycle electromagnetic pulses have been difficult to experimentally generate and to theoretically analyze. With the recent development of terahertz systems based on near infrared femtosecond lasers it has become possible to perform single cycle experiments using picosecond pulses. The work presented in this thesis lays the groundwork for the transition from investigations of ultrafast optical pulse propagation in water to similar work at terahertz frequencies.;In this thesis a variety of terahertz generation and detection methods are reviewed. Two commercial terahertz spectroscopy systems are examined in detail, improved upon and put into use. The design of a sample holder for thin, variable thickness samples of water or other highly absorbing liquid is detailed and the constructed holder is utilized in preliminary pulse measurements over a range of paths lengths. How the measured terahertz pulses spectrally and temporally change as they propagate through water is analyzed and used to extract the complex refractive index and attenuation coefficient of the tested water. Current knowledge of the molecular behavior of water in the THz frequency range of 300 GHz to 3 THz is discussed and related to experimental results. This information is also used in the preliminary development of two models. One model examines the molecular energy levels in liquid water, their effect on the propagating pulse, and the potential for the formation of precursors. The other model is based on the double Debye theory and can compare the calculated and measured pulses after propagation in both the time and frequency domains.