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The terahertz (THz) wave generation by photoconductive antennas fabricated on the low-temperature and high- temperature grown In0.5Ga0.5As semiconductor and Bi2-xSbxTe3-ySey (BSTS) topological insulator films is studied by the terahertz time-domain spectroscopy method. THz generation property of In0.5Ga0.5As layers grown by molecular beam epitaxy on GaAs substrates with (100) and (111)A crystallographic orientations is compared with THz generation capability of the BSTS films grown by the MOCVD method on a sapphire substrate. Antennas of the both types were excited by radiation of Er3+ -fiber laser at 1.56 um wavelength. THz generation by InGaAs-based antennas on (111)A GaAs substrates was 3–4 times more effective than the same antennas fabricated on the (100) wafers. It was found that the generation of THz waves was more efficient in an island film of BSTS having a total thickness of about tens nanometers with that chemical composition where the volume contribution to conductivity was suppressed. Strong amplification of the THz radiation power has been demonstrated after applying an external electric field to the topological insulator film. [ABSTRACT FROM AUTHOR]

This work contains results from studying the electro-optical properties of bulk and few-layered Van der Waals materials including intercalated graphene, phosphorene, and tungsten disulfide thin films. Different production methods and substrates are considered. The objective of the research is to assess the relevance of application of these materials in terahertz (THz) time-domain spectroscopy (TDS). Therefore, the study is conducted in the visible, NIR (near-infrared) and THz frequency ranges as the most critically in need of research when searching for effective materials for TDS. [ABSTRACT FROM AUTHOR]

The results of terahertz time-domain spectroscopy are reported for thin-film Bi, Sb and Bi1−xSbx solid solutions. The influence of film thickness and Sb content on the properties of semimetallic thin films and semimetal film/dielectric substrate structures is studied. It is shown that such semimetal/dielectric structures exhibit hyperbolic permittivity dispersion at low terahertz frequencies, and their effective refractive index can reach values less than 1 and even less than 0. These materials may be used for development of various electronic and optical components which can control the properties of terahertz radiation. [ABSTRACT FROM AUTHOR]

Broadband terahertz polarizers based on one-dimensional metal grids on carrying thin-film polymeric substrates of different thicknesses were manufactured by photolithography and investigated with terahertz time-domain spectroscopy (THz-TDS). Polarizers patterned on 4 µm polypropylene (PP) showed the best maximum power transmission >98%. Two 4-μm-PP polarizers assembled as a tandem structure exhibited minimum power transmission <1·10−4 in the spectral range of 0.2–2 THz. This corresponded to the extinction ratio >10000:1 which exceeded the dynamic range of THz-TDS. The developed polarizers were used to investigate polarization characteristics of the THz-TDS system. [ABSTRACT FROM AUTHOR]

Terahertz time-domain spectroscopy (THz-TDS) benefits from high signal-to-noise ratios (SNR), however extraction of material parameters involves a number of steps which can introduce errors into the final result. We present the use of artificial neural networks (ANN) as the first step to achieve a comprehensive approach for the extraction of the complex refractive index from THz-TDS data. The ANN shows performance superior to approximation methods and has a more straightforward implementation than root finding methods. Deep and convolutional neural networks are demonstrated to accept an entire frequency range at once, providing a tool for fitting where SNR is low, producing a more stable result. [ABSTRACT FROM AUTHOR]

The lowest frequency IR active A1(z) and E(x) modes of a ferroelectric congruent lithium tantalate crystal were studied by the broadband polarized Terahertz Time-Domain Spectroscopy using the coherent THz radiation from 0.2 to 6.5 THz. The dispersion relations of the real and imaginary parts of a polariton wave vector were determined from the complex extraordinary and ordinary refractive indices for the A1(z) and E(x) symmetry phonon-polaritons, respectively. The observed complex dispersion relations of two symmetries are in agreement within the experimental uncertainty with the calculated dispersion curves by the damped harmonic oscillator model. [ABSTRACT FROM AUTHOR]

Investigation of terahertz time domain spectroscopy (THz TDS) was made and reflection and transmission configurations were studied as a nondestructive evaluation technique. Here carbon fiber-reinforced plastics (CFRP) derived their excellent mechanical strength, stiffness and electrical conductivity from carbon fibers. Especially, the electrical conductivity of CFRP composites depends on the direction of unidirectional fibers since carbon fibers are electrically conducting while the epoxy matrix is not. The THz TDS can be considered as a useful tool using general non-conducting materials; however it is quite limited to conducting materials. In order to solve various material properties, the index of refraction (n) is derived by using the terahertz time domain spectroscopy. Also, for a 48-ply thermoplastic PPS(poly-phenylene sulfide)-based CFRP solid laminate, the terahertz scanning images were made at the angles ranged from 0° to 180° with respect to the nominal fiber axis. So, the images were mapped out based on the electrical field (E-field) direction in the CFRP solid laminates. [ABSTRACT FROM AUTHOR]

Ultra-high molecular weight polyethylene (UHMWPE) is a material increasingly used for fabricating helmet and body armor. In this work, plate specimens consolidated from thin fiber sheets in series 3124 and 3130 were examined with ultrasound, X-ray and terahertz radiation. Ultrasonic through-transmission scans using both air-coupled and immersion modes revealed that the 3130 series material generally had much lower attenuation than the 3124 series, and that certain 3124 plates had extremely high attenuation. Due to the relatively low inspection frequencies used, pulse-echo immersion ultrasonic testing could not detect distinct flaw echoes from the interior. To characterize the nature of the defective condition that was responsible for the high ultrasonic attenuation, terahertz radiation in the time-domain spectroscopy mode were used to image the flaws. Terahertz scan images obtained on the high attenuation samples clearly showed a distribution of a large number of defects, possibly small planar delaminations, throughout the volume of the interior. Their precise nature and morphology are to be verified by optical microscopy of the sectioned surface. [ABSTRACT FROM AUTHOR]

A time domain spectrometer T-ray 2000® operating in the range of 0.2-2 THz was used for Time of Flight measurements. A series of ethanol water mixtures from 10% to 90% were produced subsequently filled in polystyrene cells and analyzed in the T-ray 2000 TDS system in the reflection mode. The reflectivity of the material liquid interface is strongly influenced by the ethanol concentration in water. The reciprocal reflection coefficient of the material liquid interface was found to be a useful discriminating feature for further Probably of Detection calculations which can be used for the performance evaluation of potential THz bottle scanners. THz pulse echo (PE) measurements were performed in comparison to the established ultra sound PE technique for flaw detection of plastics. Synthetic aperture reconstructions were applied for simulated data to reconstruct the flaw shape. The results were compared with B-scan images of a high density polyethylene (HDPE) test cylinder. Existing restrictions on the quality of the back projected images and limits of the existing model are discussed in detail. [ABSTRACT FROM AUTHOR]

We present a new material parameter extraction method utilizing parallel-plate waveguides (PPWG) with terahertz time-domain spectroscopy (THz-TDS). It can be applied to natively grown samples as thin as a micron, it is repeatable and accurate, and it enables the characterization of thin films and nanostructures on conductive substrates for a variety of materials and growth conditions. The dielectric response and the complex conductivity are measured and fit with theoretic models for chemical-bath deposited zinc oxide nanowires. [ABSTRACT FROM PUBLISHER]

Terahertz wave transmission characteristic, a periodic array sub-wavelength holes slab, has been characterized by terahertz time-domain spectroscopy in the region from 0.1 to 3THz. The measurement results show that the transmittance peak of the periodic array sub-wavelength holes slab is about 35% at frequency of 2.11THz, which is consistent with that of calculation. The periodic array sub-wavelength holes slab can be employed as terahertz wave band-pass filter, which will be crucial in the implementation of future THz communications systems. [ABSTRACT FROM PUBLISHER]

We have experimentally developed a terahertz wave step attenuator (TSA) to evaluate linearity of a terahertz time-domain spectroscopy (THz-TDS) system. The TSA is constructed by stacking metalized-film attenuators (MFAs) which have different transmittance. Sputter deposition of Inconel® alloy on thin polyester films is used to fabricate the MFAs. Good repeatability and flatness of the TSA are confirmed in a transmission measurement by the THz-TDS system. This paper reports on linearity evaluation of the THz-TDS system by using the TSA. [ABSTRACT FROM PUBLISHER]

We show results on the interaction between broadband terahertz radiation and a quantum cascade laser operating at 2.87 THz. By coupling terahertz pulses into the laser’s waveguide the losses and gain in the frequency range 0.5 – 3.5 THz are determined. © 2007 American Institute of Physics [ABSTRACT FROM AUTHOR]