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Material characterization in the terahertz range is an interesting topic of research due to its great applications in material science, health monitoring, and security applications. Advances in terahertz generation, detection, and data acquisition have contributed to improved bandwidth, signal power, and signal-to-noise ratio. This enables advanced material characterization methods such as ellipsometry, which has been little explored in the terahertz frequency range, yet. Here, we introduce a comparison between material characterization with terahertz time-domain spectroscopy in transmission geometry and ellipsometry reflection geometry. Terahertz ellipsometry images were taken, showing spatially resolved refractive index estimation in the far field and higher image quality compared to single-polarization imaging. [ABSTRACT FROM AUTHOR]

The noninvasive and water‐sensitive characteristics of terahertz (THz) light make it highly attractive for in vivo studies, especially for skin applications. However, THz instrumentation has not been developed sufficiently to fully explore all the potential applications arising: current systems cannot obtain uncorrelated reflections from multiple configurations to determine the complicated structure of living tissues. Herein, this bottleneck is overcome by implementing a novel ellipsometry configuration able to efficiently provide four complementary sets of spectral ratios, significantly enhancing characterization capabilities. An accurate model of the skin is established and validated. The anisotropy of the stratum corneum (SC) caused by its cellular structure is verified both theoretically and experimentally. The in vivo response of skin on the volar forearm to occlusion is observed by the dynamic changes in the SC and the epidermis. In addition, the THz dispersion and birefringence sensitively probe the level of hydration and the cellular inhomogeneity, producing results in good agreement with microscope images and the biological processes of the SC. The presented technique offers a brand‐new functionality in extracting insightful structural information from complex systems, significantly extending the versatility of THz spectroscopy.

• A long-distance THz DFB is used to the quasi-optical THz ellipsometry. • The THz SE with the lens less reflected arm does not require additional polarizers. • The THz SE completed the thickness measurements of non-absorbent films. • The viability of a novel polarization measurement method has been demonstrated. We introduce a long-distance terahertz (THz) diffraction-free beam (DFB) to the quasi-optical THz ellipsometry. Due to the distinctive characteristics of DFBs, the reflected arm of the ellipsometer does not need a focusing lens to enhance the signal detected. Since the radiation emitted from the generator is linearly polarized, there is no need to place a polarizer on the incident arm. The THz ellipsometry with the lensless reflected arm completed the thickness measurements of non-absorbent films with thicknesses in the wavelength order. The measured values are consistent with the results measured by the micrometer. In addition, we quantitatively analyzed errors that commonly occur in this ellipsometry. The DFB generating system, which consists of two lens-axicon doublets, is fairly simple to implement. We firmly believe that the proposed approach can be easily transplanted to other types of THz ellipsometry. [ABSTRACT FROM AUTHOR]

In the past two decades, the development and steady improvement of terahertz technology has motivated a wide range of scientific studies designed to discover and develop terahertz applications. Terahertz sensing is one such application, and its continued maturation is virtually guaranteed by the unique properties that materials exhibit in the terahertz frequency range. Thin-film sensing is one branch of this effort that has enjoyed diverse development in the last decade. Deeply subwavelength sample thicknesses impose great difficulties to conventional terahertz spectroscopy, yet sensing those samples is essential for a large number of applications. In this article we review terahertz thin-film sensing, summarizing the motivation, challenges, and state-of-the-art approaches based predominately on terahertz time-domain spectroscopy. [ABSTRACT FROM AUTHOR]

The anomalous Hall effect (AHE) is a fundamental spintronic charge-to-charge-current conversion phenomenon and closely related to spin-to-charge-current conversion by the spin Hall effect. Future high-speed spintronic devices will crucially rely on such conversion phenomena at terahertz (THz) frequencies. Here, it is revealed that the AHE remains operative from DC up to 40 THz with a flat frequency response in thin films of three technologically relevant magnetic materials: DyCo 5 , Co 32 Fe 68 , and Gd 27 Fe 73 . The frequency-dependent conductivity-tensor elements σ xx and σ yx  are measured, and good agreement with DC measurements is found. The experimental findings are fully consistent with ab initio calculations of σ yx for CoFe and highlight the role of the large Drude scattering rate (≈100 THz) of metal thin films, which smears out any sharp spectral features of the THz AHE. Finally, it is found that the intrinsic contribution to the THz AHE dominates over the extrinsic mechanisms for the Co 32 Fe 68 sample. The results imply that the AHE and related effects such as the spin Hall effect are highly promising ingredients of future THz spintronic devices reliably operating from DC to 40 THz and beyond., (© 2021 The Authors. Advanced Materials published by Wiley-VCH GmbH.)