Abstract-Enhanced Terahertz Wave Generation from Cytop Antireflection–Coated DAST Crystal

Hirohisa Uchida, Chisa Koyama, Takeshi Takagi, Pei-bin Wang, Takayuki Kamei, Saroj R. Tripathi, Kodo Kawase, Kei Takeya

https://link.springer.com/article/10.1007/s10762-020-00674-6

There was no appropriate antireflection coating material for organic nonlinear optical (NLO) crystal used for terahertz wave generation; therefore, it was difficult to reduce Fresnel’s reflection loss of laser power used to excite the emitter crystal until we found that an amorphous polymer “Cytop” was applicable. Here, we demonstrate enhanced terahertz (THz) wave generation from an organic NLO crystal using a coating made from Cytop. With the Cytop coating, surface reflection losses of the excitation light were minimized, resulting in a significant improvement in THz wave generation over a wide frequency range.

Abstract-Frequency of the resonance of the human sweat duct in a normal mode of operation

Saroj R. Tripathi, Paul Ben Ishai, and Kodo Kawase

https://www.osapublishing.org/boe/abstract.cfm?uri=boe-9-3-1301&origin=search

The applications of terahertz (THz) waves have been increasing rapidly in different fields such as information and communication technology, homeland security and biomedical engineering. However, study on the possible health implications due to various biological effects induced by THz waves is relatively scarce. Previously, it has been reported that the human sweat ducts play a significant role in the interaction of the THz wave with human skin due to its coiled structure. This structure imposes on them the electromagnetic character of a helical antenna. To further understand these phenomena, we investigated the morphological features of human sweat ducts and the dielectric properties of their surrounding medium. Based upon these parameters, we estimated the frequency of the resonance of the human sweat duct in a normal mode of operation and our estimation showed that there is a broad resonance around 228 GHz. This result indicates that careful consideration should be given while designing electronic and photonic devices operating in the sub-terahertz frequency region in order to avoid various effects on human health due to these waves.

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

Non-destructive drug inspection in covering materials using a terahertz spectral imaging system with injection-seeded terahertz parametric generation and detection

Mikiya Kato,1 Saroj R. Tripathi,1,* Kosuke Murate,1 Kazuki Imayama,1 and Kodo Kawase1,2

 Graduate School of Engineering, Nagoya University, Furo-Cho, Chikusa-Ku, Nagoya, 464-8603 Japan 2 RIKEN, 519-1399, Aramaki-Aoba, Aoba, Sendai 980-0845, Japan
 * tripathi@nuee.nagoya-u.ac.jp

https://www.osapublishing.org/view_article.cfm?gotourl=https%3A%2F%2Fwww%2Eosapublishing%2Eorg%2FDirectPDFAccess%2FCA54CE12-0741-BABF-8F2A4AF83A0398A0_338151%2Foe-24-6-6425%2Epdf%3Fda%3D1%26id%3D338151%26seq%3D0%26mobile%3Dno&org=

Abstract: In 2003, we reported the first-ever development of a spectral imaging system for illicit drugs detection using a terahertz (THz) wave parametric oscillator (TPO) [K. Kawase et al., Opt. Exp. 11(20), 2549 2003]. The system has a dynamic range below four orders of magnitude, which enables it to identify reagents only through thin envelopes using spectral imaging. Recently, we succeeded in developing a high power and high sensitivity THz wave spectral imaging system using injection-seeded THz parametric generation and detection. A dynamic range in excess of 80 dB has been obtained, which is much higher than that of the 2003 system. In this study, the new spectral imaging system successfully identified reagents through thicker material than the thin envelopes used previously.
 ©2016 Optical Society of America

Abstract-Terahertz wave three-dimensional computed tomography based on injection-seeded terahertz wave parametric emitter and detector

Saroj R. Tripathi, Yuya Sugiyama, Kosuke Murate, Kazuki Imayama, and Kodo Kawase

https://www.osapublishing.org/oe/abstract.cfm?uri=oe-24-6-6433

We demonstrate a high dynamic range, three-dimensional (3-D) terahertz (THz) wave computed tomography system in which frequency tunable, Fourier transform-limited, high-power THz waves are emitted by an injection-seeded parametric source and ultrasensitive detection of THz waves is accomplished by heterodyne detection. This system covers the frequency range of 0.95 to 2.7 THz and has a maximum dynamic range in excess of nine orders of magnitude, enabling the acquisition of high-resolution 3-D tomographic images of samples with strong THz absorption. As an illustration, we obtained 3-D computed tomographic images of a pencil and a plastic product with an internal defect that demonstrates the potential applications of our imaging system in non-destructive testing and evaluation of industrial products.

© 2016 Optical Society of America

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