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

TL;DR

This paper investigates how phase inaccuracies, caused by placement mismatches in reflection-type THz-TDS, significantly affect the accuracy of the extracted complex refractive index, especially beyond 3 μm mismatch.

Contribution

It provides a quantitative analysis of phase inaccuracy effects on refractive index extraction in reflection-type THz-TDS, highlighting the importance of precise sample placement.

Findings

Errors increase with placement mismatch beyond 3 μm

Phase inaccuracy impacts free and bound carrier systems

Guidelines for minimizing measurement errors

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.