Low-noise, rapid and ultrabroadband terahertz time-domain ellipsometry enabled by spintronic terahertz emitters

Electromagnetic radiation in the terahertz (THz) frequency range (0.3-30 THz) is a powerful tool for material spectroscopy and characterization in a contact-free, non-ionizing and non-destructive way. An essential application is the contact-free measurement of the complex-valued reflectivity and, ideally, refractive index of materials. Such knowledge is essential in condensed-matter research (for characterization of, e.g., the conduction-electron concentration and scattering in semiconductors, of optical phonons in insulators and magnons in antiferromagnets) and in applied settings. Ideally, THz reflectivity measurements should be (1) ultrabroadband (covering two decades from 0.3 to 30 THz), (2) user-friendly and offer (3) high precision and low noise. However, requirements (1)-(3) are not fulfilled by current approaches. The goal of T-SPINDEX is to build a prototype THz time-domain reflectivity spectrometer to determine the THz refractive index of materials rapidly. Features (1)-(3) are achieved altogether by using an innovative laser-driven coherent THz source, a spintronic THz emitter.