This book documents novel techniques in the area of field-resolved spectroscopy (FRS) in the terahertz range of the electromagnetic spectrum. In FRS, the electric field of atypically very broadbandlong-wavelength test wave is scanned using non-linear gating processes with short-wavelength light pulses. Measuring the oscillating field of the test wave provides direct, time-resolved insights into its formation, and into light-matter interactions. The first part of the thesis surveys the conceptual background of the technologies used, introducing frequency combs, interferometry, FRS and terahertz spintronics. In the second part, the dissertation addresses the challenge of precisely calibrating the delay axis during the scanning process for FRS. Employing a novel, multi-color interferometric arrangement, the authors implementation surpasses the temporal precision of state-of-the-art terahertz-FRS by approximately one order of magnitude. The last part of the thesis deals with spintronic terahertz emitters as a broadband alternative to photoconductive switches. One highlight is the development, demonstration and characterization of fiber-tip spintronic terahertz emittersthe worlds smallest terahertz emitters. The author then integrated these emitters into an s-SNOM system and successfully introduced a spatiotemporally resolved terahertz emission nanoscopy with nanometer spatial and femtosecond temporal resolution, opening new avenues in optical sensing.
