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Terahertz (THz) spectroscopy has been put forth as a non-contact, analytical probe to characterize the intermolecular interactions of biologically active molecules, specifically as a way to understand, better develop, and use active pharmaceutical ingredients. An obstacle towards fully utilizing this technique as a probe is the need to couple features in the THz regions to specific vibrational modes and interactions. One solution is to use density functional theory (DFT) methods to assign specific vibrational modes to signals in the THz region, coupling atomistic insights to spectral features. Here, we use open source planewave DFT packages that employ ultrasoft pseudopotentials to assess the infrared (IR) response of organic compounds and complex co-crystal formulations in the solid state, with and without dispersion corrections. We compare our DFT computed lattice parameters and vibrational modes to experiment and comment on how to improve the agreement between theory and modeling to allow for THz spectroscopy to be used as an analytical probe in complex biologically relevant systems. 

Abstract Terahertz (THz) imaging has attracted much attention within the past decade as an emerging nondestructive evaluation technique. In this paper, we present a novel Laser-based Metamaterial Fabrication (LMF) process for high-throughput fabrication of transparent conducting surfaces on dielectric substrates such as glass, quartz and polymers to achieve tunable THz bandpass characteristics. The LMF process comprises two steps: (1) applying ultrathin-film metal deposition, with a typical thickness of 10 nm, on the dielectric substrate; (2) creating a ~100-micron feature pattern on the metal film using nanosecond pulsed laser ablation. Our results demonstrate the use of laser-textured ultra-thin film with newly integrated functional capabilities: (a) highly conductive with ~20 Ω/sq sheet resistance, (b) optically transparent with ~70% transmittance within visible spectrum, and (c) tunable bandpass filtering effect in the THz frequency range. A numerical analysis is performed to help determine the fundamental mechanism of THz bandpass filtering for the LMF-built samples. The scientific findings from this work render an economical and scalable manufacturing technique capable of treating large surface area for multi-functional metamaterials. 

Abstract Development of terahertz (THz) sources, detectors, and optical components has been an active area of research across the globe. The interest in THz optoelectronics is driven by the various applications they have enabled, such as ultrawide‐band communication systems, air‐ and space‐borne astronomy, atmospheric monitoring, small‐scale radar, airport security scanners, ultrafast nanodevices, and biomedical imaging and sensing. Here, the aim is to provide a comprehensive review of THz bandpass metamaterials focusing on several areas. First, the design fundamentals and geometrical patterns of THz bandpass metamaterials are summarized. Second, fabrication methods of THz bandpass metamaterials are reviewed, including typical micro‐ and nanofabrication techniques and laser micromachining techniques. More importantly, different engineering methods are reviewed for tuning and modulation of the THz transmission resonance for these metamaterials. Both passive and active modulation methods are included in this discussion; the passive method involves changes in the geometrical pattern of the filter material, and the active method performs in situ modulation of properties by applying an external physical field. Finally, the potential applications and prospects for future research of THz bandpass metamaterials are discussed.