High-precision THz-TDS via self-referenced transmission echo method

Abstract

Terahertz time-domain spectroscopy (TDS) is a powerful characterization technique which allows for the frequency-dependent complex refractive index of a sample to be determined. This is achieved by comparing the time-domain of a pulse transmitted through air to a pulse transmitted through a material sample; however, the requirement for an independent reference scan can introduce errors due to laser fluctuations, mechanical drift, and atmospheric absorption. In this paper, we present a method for determining complex refractive index without an air reference, in which the first pulse transmitted through the sample is compared against the “echo”, where the internal reflections delay the transmission of the echo pulse. We present a benchmarking experiment in which the echo reference method is compared to the traditional air method, and show that the echo method is able to reduce variation in real refractive index.

Reference-free THz-TDS conductivity analysis of thin conducting films

“…In fact, an echo signal from the sample measurement, when compared with the direct transmitted signal from the same transmission-mode scan, can lead to the retrieval of sample properties without the need for the standard reference scan. Very recently, this type of reference-free methodology has been applied to determine the refractive index and wave impedance of dielectrics [15].…”

Optically Defined Reconfigurable THz Metasurfaces using Graphene on Iron‐Doped Lithium Niobate

“…The lithium niobate slab is modeled with frequencydependent values of complex refractive index, which we have measured via THz TDS, and reported in detail previously. [52] The graphene conductivity (σ) and scattering time (τ) are calculated from the Kubo equations [53] as shown in Equation ( 1) and ( 2), respectively…”

“…The lithium niobate slab is modeled with frequency‐dependent values of complex refractive index, which we have measured via THz TDS, and reported in detail previously. [ 52 ] The graphene conductivity ( σ ) and scattering time ( τ ) are calculated from the Kubo equations [ 53 ] as shown in Equation () and (), respectivelywhere e is the electron charge, t is the graphene thickness (1 nm), ω is the radial frequency, μ is the graphene charge carrier mobility, and v F is the Fermi velocity (10 8 cm s −1 ).…”

Case studies of electrical characterisation of graphene by terahertz time-domain spectroscopy

“…Recently, it has been shown that it is also possible to perform reference-free extraction of dielectric and electrical properties of substrates and thin conducting films from THz-TDS measurements [28,29]. This is achieved by comparing individual transients from only the sample waveform, which means that the reference measurement can be omitted and furthermore decreases errors from signal fluctuations originating from the measurement setup such as timing jitter [26], periodic sampling errors [30], and uneven stage movement.…”