Abstract-Terahertz imaging with room-temperature terahertz difference-frequency quantum-cascade laser sources

Atsushi Nakanishi, Kazuue Fujita, Kazuki Horita, and Hironori Takahashi

Fig. 1 Properties of THz DFG-QCL at –30 °C: (a) Spectrum, (b) far-field profile, (c) horizontal and vertical sections of the beam profile.

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-27-3-1884

We demonstrate high-quality non-destructive imaging using a broadband terahertz quantum cascade laser source based on Cerenkov difference-frequency generation. The source exhibited ultra-broadband terahertz emission spectra, as well as a single-lobed Gaussian-like far-field pattern at –30 °C. These features allowed us to build a compact imaging system with a high spatial resolution, from which a nearly theoretical minimum beam spot size was obtained. As a result, we achieve well-resolved, high-contrast images of objects obscured by opaque materials. We also achieved terahertz imaging with the THz DFG-QCL operated at room temperature.

© 2019 Optical Society of America under the terms of the OSA Open Access Publishing Agreement

Abstract-Terahertz optical material based on wood-plastic composites

Atsushi Nakanishi and Hironori Takahashi

Fig. 1 Photograph of WPC samples having wood powder contents between 0 wt% and 60 wt% after a drying process.

https://www.osapublishing.org/ome/abstract.cfm?uri=ome-8-12-3653

We investigated the terahertz optical properties of wood-plastic composites (WPCs) having varying wood powder contents. To evaluate the influence of water uptake, we measured WPC samples under conditions where the water content of each WPC sample was controlled. We found that the refractive indexes and the absorption coefficients of the WPCs increased with accumulating wood powder content. Also, we found that the optical properties of the WPCs were almost constant for wood powder contents ranging from 0 wt% to 40 wt%, even in a high-humidity environment. WPCs are promising materials for terahertz optical components.

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

Abstract-Tunable Terahertz Device Using Refractive Index Control

Atsushi Nakanishi, Takashi Yasuda, Kazuki Horita, Hironori Takahashi,

https://link.springer.com/article/10.1007%2Fs10762-017-0430-x

We measured the thermal dependencies of the refractive index and the absorption coefficient of high-resistivity silicon. We found that the refractive index varied slightly with temperature, and the absorption coefficient was very low and remained approximately constant as the temperature was changed. As a result, the conditions for terahertz propagation in silicon could be controlled by changing the refractive index without any absorption loss. As one application of this effect, we developed a terahertz time delay generator that can generate a terahertz time delay by changing the temperature of the medium through which the terahertz beam passes, without the need for any mechanical delay. We demonstrated generation of a terahertz time delay of approximately 6.6 ps.