Abstract-THz imaging techniques for nondestructive inspections

Kodo Kanwkse,  Takayuki Shibuya, Shin'ichiro Hayashi, Koji Suizu

https://www.sciencedirect.com/science/article/pii/S1631070510000423

We have suggested a wide range of real-life applications using novel terahertz imaging techniques. A high-resolution terahertz tomography has been demonstrated by ultra short terahertz pulses using optical fiber and a nonlinear organic crystal. We also describe a nondestructive inspection system that can monitor the soot distribution in a ceramic filter using millimeter-to-terahertz wave computed tomography. Further, we report on the thickness measurement of very thin films using high-sensitivity metal mesh filter. These techniques are directly applicable to the nondestructive testing in industries.

Abstract-Terahertz Pulse Reflection Imaging Using the Time-Domain Correlating Synthesis Method

Ryo Toh ;  Koji Suizu ;  Yuya Tojima

http://ieeexplore.ieee.org/document/7908987/

The synthetic aperture method is an attractive technique for terahertz nondestructive imaging without strict restraints on the beam form or the Rayleigh length of focus. However, the limitation of the aperture of the receiver array results in distortion and restricted lateral resolution of the reconstructed image. This paper introduces a nonlinear imaging processing principle, the correlating synthesis method, which has been applied in ultrasonic measurements. Using a pulse reflection mode terahertz time-domain spectrometry system and pulse compression preprocessing, we reconstructed images of metal cylinders. The results of comparisons with a synthetic aperture method verify the efficiency of the correlating synthesis method for improving the lateral resolution and eliminating fake images.

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.