Abstract-Terahertz Fano-like resonators based on free-standing metallic wire woven meshes

Dejun Liu, Borwen You, Toshiaki Hattori

https://arxiv.org/abs/2001.01965

Most periodic terahertz (THz) structures need a substrate to support; thus, additional absorption occurs, resulting in a low quality (Q) factor. Free-standing structures that do not require any holder or substrate show high levels of flexibility and stretchability and hence are well-suited for THz applications. In this work, a free-standing THz metal structure consisting of metallic wire woven meshes is proposed and demonstrated. Experimental and numerical results exhibit that this metallic mesh achieves a sharp Fano-like resonance dip, which has not been found in previous studies. Investigation results indicate that the high Q Fano-like resonance dip comes from the single-layer metal bent wire because of its bending effect. The resonance field longitudinally covers the input and output end faces due to the large field volume of the woven meshes and benefits from near-field sensing applications.

Abstract-Spectroscopy and sensing of fluid using terahertz waves

Toshiaki Hattori,  Katsuyoshi Aoki,  Borwen You,  Ja-Yu Lu,  Chin-Ping Yu

https://www.spiedigitallibrary.org/conference-proceedings-of-spie/10826/108260K/Spectroscopy-and-sensing-of-fluid-using-terahertz-waves/10.1117/12.2505842.short?SSO=1

Understanding of terahertz spectroscopic properties of materials is crucially important for applications of terahertz waves in sensing. Spectroscopic properties of water-rich media, such as biological tissues, gels, and aqueous solutions, are strongly affected by the amount and the dynamics of water in them. Terahertz spectroscopical measurements can clarify the dynamical and/or structural characteristics of water molecules in the hydrogen-bond network in these media. We studied the dynamical properties of water around protein molecules and polymers in aqueous solutions using terahertz spectroscopic measurements. Sensing of liquid using a terahertz waveguide composed of a metal rod array will also be described.

© (2018) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only

Abstract-Investigation of spectral properties and lateral confinement of THz waves on a metal-rod-array-based photonic crystal waveguide

Borwen You, Dejun Liu, Toshiaki Hattori, Tze-An Liu, and Ja-Yu Lu

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-26-12-15570

Terahertz (THz) waves laterally confined in a 1 mm-thick microstructured planar waveguide are demonstrated on a free-standing metal rod array (MRA), and one apparent rejection band of a transmission spectrum, resembling the bandgap of a photonic crystal, is found in 0.1–0.6 THz. The visibility of the photonic bandgap in the spectral width and power distinction can be manipulated by changing the MRA geometry parameters, including the rod diameter, the interspace between adjacent rods, and the propagation length based on the interactive MRA-layer number. THz transmission ratio enhanced by a large interactive length is verified in 30 MRA layers due to the longitudinally resonant guidance of transverse-magnetic-polarized waveguide modes along the MRA length, which is critical to the interspace width of adjacent rods and the metal coating of the rod surface. For an MRA with respective rod diameter and interspace dimensions of about 0.16 and 0.26 mm, the highest transmission of the guided resonant THz waves are performed at 0.505–0.512 THz frequency with strong confinement on the metal rod tips and a low scattering loss of 0.003 cm−1.

© 2018 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz artificial material based on integrated metal-rod-array for phase sensitive fluid detection

Borwen You, Ching-Yu Chen, Chin-Ping Yu, Tze-An Liu, Toshiaki Hattori, and Ja-Yu Lu

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-25-8-8571

A terahertz artificial material composed of metal rod array is experimentally investigated on its transmission spectral property and successfully incorporated into microfluidics as a miniaturized terahertz waveguide with an extended optical-path-length for label-free fluidic sensing. Theoretical and experimental characterizations of terahertz transmission spectra show that the wave guidance along the metal rod array originates from the resonance of transverse-electric-polarized waves within the metal rod slits. The extended optical path length along three layers of metal-rod-array enables terahertz waves sufficiently overlapping the fluid molecules embedded among the rods, leading to strongly enhanced phase change by approximately one order of magnitude compared with the blank metal-parallel-plate waveguide. Based on the enhanced phase sensitivity, three kinds of colorless liquid analytes, namely, acetone, methanol, and ethanol, with different dipole moments are identified in situ using the metal-rod-array-based microfluidic sensor. The detection limit in molecular amounts of a liquid analyte is experimentally demonstrated to be less than 0.1 mmol, corresponding to 2.7 μmol/mm2. The phase sensitive terahertz metal-rod-array-based sensor potentially has good adaptability in lab-chip technology for various practical applications, such as industrial toxic fluid detection and medical breath inspection.

© 2017 Optical Society of America

Abstract-Salt effects on the picosecond dynamics of lysozyme hydration water investigated by terahertz time-domain spectroscopy and an insight into the Hofmeister series for protein stability and solubility

Katsuyoshi Aoki,^a   Kentaro Shiraki^b and   Toshiaki Hattori*^a  

http://pubs.rsc.org/en/content/articlelanding/2016/cp/c5cp06324h#!divAbstract

Phys. Chem. Chem. Phys., 2016, Advance Article

DOI: 10.1039/C5CP06324H
Received 18 Oct 2015, Accepted 03 May 2016
First published online 19 May 2016

The addition of salts into protein aqueous solutions causes changes in protein solubility and stability, whose ability is known to be ordered in the Hofmeister series. We investigated the effects of Hofmeister salts on the picosecond dynamics of water around a lysozyme molecule using terahertz time-domain spectroscopy. The change in the absorption coefficient for 200 mg mL⁻¹ lysozyme aqueous solution by the addition of salts was found to depend on the salts used, whereas that for pure water was almost independent of salts. From the difference in the salt concentration dependence for various salts, it has been found that chaotropic anions make the dynamics of water around the lysozyme molecule slower, whereas kosmotropic anions make the dynamics faster. The ability of an anion to slow down the water dynamics was found to have the following order: SCN⁻ > Cl⁻ > H₂PO₄⁻ > NO₃⁻ ≈ SO₄²⁻. This result indicates that the effects of anions on the dynamics of water around the lysozyme molecule are the opposite of those for bulk water. This finding agrees with a prediction from a molecular model proposed by Collins [K. D. Collins, Methods, 2004, 34, 300]. The results presented here are compared with the results from preferential interaction studies and the results from sum frequency generation spectroscopy. These discussions have led to the conclusion that the picosecond dynamics of protein hydration water strongly contributes to protein stability, whereas electrostatic interactions between protein molecules contribute to protein solubility.