Abstract-Broadband high-resolution terahertz single-pixel imaging

Adam Vallés, Jiahuan He, Seigo Ohno, Takashige Omatsu, Katsuhiko Miyamoto

https://arxiv.org/abs/2006.05877

We report a simple single-pixel imaging system with a low mean squared error in the entire terahertz frequency region (3-13 THz) that employs a thin metallic ring with a series of directly perforated random masks and a subpixel mask digitization technique. This imaging system produces high-quality reconstructed images with resolutions of up to 320 x 320 pixels. It can be extended to develop advanced imaging systems in the near-ultraviolet to terahertz region.

Abstract-Terahertz Phonon Modes of Highly Efficient Electro-Optic Phenyltriene OH1 Crystals

Jongtaek Kim, Seung-Heon Lee, Seung-Chul Lee, Mojca Jazbinsek, Katsuhiko Miyamoto, Takashige Omatsu,Yoon Sup Lee, and O-Pil Kwon

J. Phys. Chem. C, Just Accepted Manuscript

DOI: 10.1021/acs.jpcc.6b07979

Publication Date (Web): October 4, 2016

Copyright © 2016 American Chemical Society

http://pubs.acs.org/doi/abs/10.1021/acs.jpcc.6b07979

Understanding the origin of phonon modes of highly efficient electro-optic crystals is very important for designing materials and for optimizing their photonic applications. Here we investigate the origin of phonon modes in the 0.1–15 THz range of the benchmark electro-optic OH1 (2-(3-(4-hydroxystyryl)-5,5-dimethylcyclohex-2-enylidene)malononitrile) crystal, interesting due to its large electro-optic coefficient and high THz-wave generation efficiency. The phonon modes (and vibrational absorption properties) of OH1 crystals are evaluated theoretically by periodic density functional theory and also experimentally by THz absorption spectroscopy. The theoretical calculations are well-matched with experimental results. The THz absorption properties are highly anisotropic; the amplitude of vibrational absorption is largest along the polar c-axis compared to the other two crystallographic axes. For comparison, vibrational absorption modes of the OH1 molecule in gas phase are also calculated. The calculated vibrational absorption spectrum of OH1 crystalline powder appears similar to that of the OH1 molecule in gas phase. However, the molecular vibrational motions in crystalline state are coupled motions of vibrational motions in gas phase. Interestingly, the vibrational mode of the torsion of the O-H bond with the largest absorption strength in gas phase is in crystal inhibited due to the crystal field effect. The origin of intense phonon modes of OH1 crystals is mainly related to relatively strong distortions of the push-pull -conjugated system including electron donor and acceptor groups.

Abstract-Evaluation of polarized terahertz waves generated by Cherenkov phase matching

Takuya Akiba, Yasuhiro Akimoto, Koji Suizu, Katsuhiko Miyamoto, and Takashige Omatsu  »View Author Affiliations

Applied Optics, Vol. 53, Issue 8, pp. 1518-1522 (2014)
http://dx.doi.org/10.1364/AO.53.001518

http://www.opticsinfobase.org/ao/abstract.cfm?uri=ao-53-8-1518

We report terahertz (THz) wave generation by satisfying Cherenkov phase-matching condition in both s and ppolarizations. A dual-wavelength optical parametric oscillator is constructed from two potassium titanium oxide phosphate crystals pumped by a frequency-doubled Nd:YAG laser. By rotating the orientation of both a lithium niobate crystal (LiNbO3) and the polarization of the pump waves, the polarization of the THz wave changes. Due to the difference in the refractive index and absorption, the output power for p polarization is one tenth that for s polarization. A tuning range from 0.2 to 6.5 THz is obtained for s polarization, and from 0.2 to 4.2 and 5.4 to 6.9 THz for p polarization. The extraction efficiency is improved by changing the angle of prism for p polarization, and a large phase change occurs at total internal reflection. Consequently, p-polarized THz waves are optimal for spectroscopic applications.

© 2014 Optical Society of America

Abstract-THz-wave sensing via pump and signal wave detection interacted with evanescent THz waves

Takuya Akiba, Naoya Kaneko, Koji Suizu, Katsuhiko Miyamoto, and Takashige Omatsu  »View Author Affiliations

http://www.opticsinfobase.org/ol/abstract.cfm?uri=ol-38-18-3687

We report a novel sensing technique that uses an evanescent terahertz (THz) wave, without detecting the THz wave directly. When a THz wave generated by Cherenkov phase matching via difference frequency generation undergoes total internal reflection, the evanescent THz wave is subject to a phase change and an amplitude decrease. The reflected THz wave, under the influence of the sample, interferes with the propagating THz wave and the changing electric field of the THz wave interacts with the electric field of the pump waves. We demonstrate a sensing technique for detecting changes in the electric field of near-infrared light, transcribed from changes in the electric field of a THz wave.