Terahertz (THz) spectroscopy and imaging have emerged as important tools for identification and classification of various substances, which exhibit absorption characteristics at distinct frequencies in the THz range. The spectral fingerprints can potentially be distorted or obscured by electromagnetic scattering caused by the granular nature of some substances. In this paper, we present THz time domain transmission measurements of granular polyethylene powders in order to investigate an effective medium theory that yields a parameterized model, which can be used to estimate the empirical measurements to good accuracy.

Abstract-The scattering of terahertz radiation from the granular nature of a sample can potentially distort or obscure its characteristic spectral features. Several techniques have been proposed to reduce the effects of scattering in terahertz timedomain spectroscopy (THz-TDS) measurements, that usually require a complex measurement apparatus or rely on specific information about the sample under study. However, in realworld applications a priori information of the sample is not always known and therefore the applicability of these techniques may be limited. In this letter, we present a method for estimating and mitigating scattering effects in THz-TDS measurements for samples made of material exhibiting sharp and sparse absorption features, without requiring information of its granularity, refractive index, and density.

Frequency dependent absorption of a given material at distinct frequencies in the terahertz (THz) range is commonly used as a spectral fingerprint for material identification and classification. However, in the presence of strong scattering, these features can often become distorted or altered. Thus, there is an important need to understand how scattering from a sample alters the THz signal. In this letter, we propose an iterative algorithm that builds on the effective field theory proposed by P. C. Waterman and R. Truell [J. Math. Phys. 2, 512–537 (1961)] and offers a rather simple and computationally efficient method for accurately explaining the multiple scattering response of a medium.

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A hollow core antiresonant photonic crystal fiber (HC-ARPCF) with metal inclusions is numerically analyzed for transmission of terahertz (THz) waves. The propagation of fundamental and higher order modes are investigated and the results are compared with conventional dielectric antiresonant (AR) fiber designs. Simulation results show that broadband terahertz radiation can be guided with six times lower loss in such hollow core fibers with metallic inclusions, compared to tube lattice fiber, covering a single mode bandwidth (BW) of 700 GHz.