Influence on extracted complex refractive index from phase inaccuracy of reflection-type THz-time-domain spectroscopy

Abstract: Reflection-type terahertz (THz) time-domain spectroscopy (THz-TDS) enables the measurement of optical properties of opaque samples in the THz frequency range, e.g., carrier density and mobility. In this study, we examine the influence of phase inaccuracy on the extracted complex refractive index from reflection-type THz-TDS. Phase inaccuracy often arises from the placement mismatch between the perfect reflector, serving as the reference, and the target samples in reflection-type THz-TDS. By considering two representative systems, where free and bound carriers dominate optical properties, and introducing arbitrarily shifted placement mismatch, we confirm that significant errors in the extracted complex refractive index occur when the mismatch position exceeds 3 {\mu}m.