Ultrafast Field Emission Processes with Terahertz and Mid-Infrared Radiation

This thesis presents an experimental and theoretical investigation of electron field emission from metallic micro antennas in the Terahertz (THz) and mid-infrared (mid-IR) regions of the electromagnetic spectrum and their potential application in ultrafast spectroscopy and mid-IR detection. The thesis begins by presenting the fundamental knowledge about THz generation and detection, followed by an introduction to the Fowler-Nordheim field emission theory. After the fundamentals for this thesis are explained, the performed experiments, results, and analyses are presented. The first experimental part of the thesis focuses on the application of metallic field emitters for THz radiation and investigates the electron field emission into gaseous and liquid samples. The results demonstrate that electrons can be field emitted into those media. The gaseous samples show a good agreement with the Fowler-Nordheim theory. However, the emission into the liquid samples deviates from the expected Fowler-Nordheim trend, which is attributed to the influence of other field-induced effects. A correction constant is introduced, taking these field effects into account. Additionally, the study presents a simple simulation for electron acceleration in gaseous environments and showcases the importance of the potential barrier shape in the Fowler-Nordheim emission, and gives insights into realistic parameter choice in the field emission theory. The second study presented in this thesis examines a novel mid-IR photo-multiplier tube (PMT) based on field emission nano-antennas. The study characterizes the PMT with respect to its wavelength-dependent response, which is as well simulated using COMSOL®. As a potential use case, interferometric autocorrelations with the PMT as the detector are performed and analyzed by simulations of the autocorrelation traces. The performance of the PMT for
application in autocorrelations measurements is compared to standard 2-photon-based midIR autocorrelations. Overall, this thesis presents important findings that contribute to the understanding of electron field emission from metallic micro-antennas and their potential applications in ultrafast spectroscopy and mid-IR detection. The research emphasizes the importance of understanding the electron field emission process and the influence of other field-induced effects on the emission process. Additionally, the novel mid-IR PMT based on field emission nano-antennas shows potential for use in mid-IR detection applications. These findings could have significant implications for the development of new technologies in the THz and mid-IR regions.