Abstract-Cherenkov-phase-matched nonlinear optical detection and generation of terahertz radiation via GaAs with metal-coating

Ramon Delos Santos, Shinpei Ozawa, Valynn Mag-usara, Syougo Azuma, Anthony Tuico, Vernalyn Copa, Arnel Salvador, Kohji Yamamoto, Armando Somintac, Kazuyoshi Kurihara, Hideaki Kitahara, Masahiko Tani, and Elmer Estacio

https://www.osapublishing.org/oe/fulltext.cfm?uri=oe-24-22-24980&id=352625

Terahertz (THz) wave detection and emission via Cherenkov-phase-matched nonlinear optical effects at 1.55-μm optical wavelength were demonstrated using a GaAs with metal-coating (M-G-M) and bare GaAs as a reference sample in conjunction with a metallic tapered parallel-plate waveguide (TPPWG). The metal-coated GaAs is superior to the bare wafer both as a THz electro-optic detector and as an emitter. Significant improvements in the detection and emission efficiency were obtained by utilizing a metal-coating due to better confinement and lower loss of the THz waves propagating in the M-G-M compared with bare GaAs.

© 2016 Optical Society of America

Abstract-Sub-terahertz imaging using time-domain signals obtained with photoconductive spiral antennas

Osamu Morikawa, Kohji Yamamoto, Kazuyoshi Kurihara, Masahiko Tani, Fumiyoshi Kuwashima, and Masanori Hangyo
https://www.osapublishing.org/josab/abstract.cfm?uri=josab-33-9-1940

A sub-terahertz time-domain spectroscopic system with spiral antennas, which have high efficiency in the sub-THz region, was applied to imaging. In the time-domain signals, there were several peaks with various widths. Images were obtained by translating samples at the focus of the sub-THz beam with the time delay fixed at certain positions while monitoring the signal. At the edge of the metal patterns, the signal basically showed step-like variations, which were sometimes accompanied by overshoot structures (peaks and dips) depending on the time-delay position. The overshoot can be utilized to make the images sharper. The time-delay position can be adjusted to make the step height zero and produce images that contain only the overshoot, which can be transformed into images of the edge lines of the metal pattern. In addition, an image of the watermark on a 1000-yen bill was obtained. The image contrast caused by the small variation of the bill paper thickness was enhanced by locating the time delay at the position where the signal shows maximum sensitivity to the phase shift.

© 2016 Optical Society of America

Full Article  |  PDF Article