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We propose a novel method for establishing and aligning a THz ellipsometry system and for calibrating ellipsometry signals for precise THz ellipsometry measurements. The method significantly improves the THz ellipsometry accuracy compared to the current publications.
The water diffusivity of occluded human stratum corneum (SC) is estimated by standard terahertz reflection spectroscopy and a SC swelling diffusion model. We find that the water diffusivity in occluded skin is higher than that in steady state at the onset of occlusion. This method is potentially useful for non-invasive diagnosis of human skin conditions.
We propose a novel reference-acquisition method that provides precise phase alignment for terahertz imaging. The method significantly improves the accuracy of the extracted sample optical properties and greatly improves the experimental efficiency compared to traditional reference methods.
We have experimentally realized a broadband THz modulator in a total internal reflection geometry using SiO2/Si gated monolayer graphene. The modulation depth in our device is up to 83% over the range of 0.2–0.6 THz, and can be further improved by extending the size of our modulator and using multiple reflections.
We report ultra-broadband, easily tuned, and highly efficient metamaterial terahertz wave retarders that are able to convert linear polarization into circular and elliptical polarization states. The broadband nature arises from the combination of the plasmonic effect and the property of polarization conversion. The dielectric response of the metamaterial microstructure and the angular phase dispersion...
In this paper we show how the act of measuring skin in vivo using a standard terahertz reflection imaging system affects the terahertz response. We found that even 5 seconds occlusion by the imaging window caused subtle changes in the THz response. As the occlusion time increases, the skin's surface water content increases which causes the refractive index of the skin to increase. This in turn leads...
Terahertz light is so strongly absorbed by water that a subtle change in sample water content, be it due to the presence of a medical condition or due to environmental conditions or storage, can affect the terahertz response. This makes it challenging to devise experimental protocols to investigate potential biomedical applications of terahertz imaging and spectroscopy. In this work we detail some...
An opaque state that appears to be analogous to the electromagnetically induced transparency (EIT) phenomenon is generated using an asymmetric dimer of rectangular holes. By imaging in the near-field for the first time these metal hole arrays (MHAs) we find that the opaque state may be a result of constructive interference between the surface plasmon polaritons (SPPs) launched along the surface of...
For ex vivo biological imaging, sample handling can affect image contrast. We investigate the effects of the slow freeze-thaw cycle on the THz properties of porcine lean and fat tissues. Lean tissues showed a significant decrease in the refractive index after the freeze-thaw cycle while there was no significant change observed in THz properties of fat tissues.
Terahertz (THz) metamaterials have recently attracted much interest due to their ability to tune propagation properties using sub-wavelength structures. In this paper we demonstrate the first metamaterial device developed by patterning a vanadium dioxide (VO2) wire-grid structure onto a c-sapphire substrate. Temperature and polarization dependent THz time-domain spectroscopy transmission measurements...
We have derived the Fresnel reflection coefficients incorporating both total internal reflection (TIR) and a conductive interface. Using this result we show that the reflectance in the TIR regime has a larger dependency on the optical conductivity of the conductive layer than the transmittance in the normal incidence regime. This suggests that a TIR prism with a controllable conductive layer such...
We have simulated and fabricated a liquid crystal based terahertz spatial light modulator. Our patented terahertz in plane and terahertz out of plane (TIP-TOP) switching technique enables the liquid crystal cell to be switched over two orders of magnitude faster than ordinary methods thus making it suitable for use in terahertz spatial light modulation.
Terahertz (THz) neutral density (ND) filters are a useful components in THz system, and have recently attracted s much interest. In this paper we report on the potential of d PEDOT/PSS conductive polymer thin film doped with a polar i organic compound dimethylformamide (DMF) as a THz ND filter. The THz transmission through the thin film is controlled by the DMF doping concentration.
We propose an adaptive sampling method to reduce the average sampling time for THz-TDS. The sampling time improves up to threefold as the new approach takes only 20% to 30% of samples compared to conventional sampling acquisition, depending on the algorithms and experimental parameters. Sampling adaptively can capture peak to peak amplitudes accurately, making this technique useful in time critical...
Interest in bio terahertz research has recently been increasing worldwide. Major topics include cancer diagnosis, skin studies, tissue characterization and protein dynamics. Although terahertz technology has great potential in the biomedical and biological research fields, several obstacles have to be overcome before it can be used commercially and clinically. This paper talks about the current state...
Structural evolution with temperature of tetraphenylethene (TPE) is followed using THz-TDS. The observed changes in the terahertz spectra are rationalized by performing DFT calculations on experimentally determined low and high temperature crystal structures, thus allowing the changes to be rationalized in terms of the subtle changes in the supramolecular structure.
Terahertz time domain spectroscopy has been used to characterize various tissues in biomedical research to date. In this paper the terahertz properties of three groups of rat skin tissues treated with different injections (normal saline control, high dose of Dotarem, and high dose of Omniscan) are measured. The difference in terahertz properties of the tissues can be clearly observed from the results.
We report the terahertz spectrum of a high birefringence liquid crystalline mixture 2002 from 0.2 to 1.6 THz, using terahertz time domain spectroscopy (THz-TDS). Furthermore, the phase transition from nematic to isotropic phases was observed using temperature-dependent THz-TDS.
We have developed a novel wire grid polarizer on a thin film substrate to overcome multiple reflection issues found in conventional polarizers. In this paper, we show how our polarizer can be used to characterize the vertical and horizontal polarization components of a THz photoconducting antenna.
Fiber based THz systems are preferred because of their compactness and flexibility. This paper points out the ‘double pulse’ phenomenon which is encountered when exploring fiber-based systems. Debugging methods are given in the hope of helping researchers who may experience the same problem.
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