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Terahertz imaging of dried red pepper and shrimp

Injection seeded THz-wave parametric generator; is-TPG


Morphology of human sweat ducts observed by optical coherence tomography


Evolved injection seeded THz-wave spectrometer for mail inspection[1]

    In 2003, we demonstrated a first ever non-destructive terahertz spectroscopic imaging of illicit drugs hidden in envelopes using a widely tunable THz-wave parametric source, though its dynamic range at that time was less than four orders[2]. Recently, we have realized ten orders of dynamic range with an evolved injection seeded THz-wave spectrometer. Now we can detect drugs under much thicker obstacles than before[1]. In this report, we introduce related topics; Enhanced tuning range up to 5 THz, 100dB dynamic range THz detection using near infrared detector, Comparison between is-TPG spectrometer and TDS.


   For years, we have worked on the development of a high-power THz-wave source, based on parametric processes in a LiNbO3 crystal. In 2001, we created an injection-seeded THz-wave parametric generator (is-TPG) with 300mW output [3]. Recently, the peak output power of is-TPG approached 100 kW [4] by introducing a new pump laser with shorter pulse width. However, the tunability of is-TPG was still limited less than 3 THz due to the strong absorption loss inside the LiNbO3 crystal. In order to suppress this absorption loss, we tilted the LiNbO3 crystal slightly so that the THz waves were generated at the very near-surface of the crystal. The pump beam was totally reflected at the crystal surface where the THz-wave was generated. Thus we have realized much wider tunability up to 5 THz.


    In the detection section of our system, THz-wave was converted back into near infrared beam by nonlinear optical wavelength conversion. Since the detection methodologies in optical frequency region are well established and high sensitive near infrared detectors are readily available, we were able to measure the extremely small THz-wave output by measuring the power of converted near infrared beam. In order to measure the dynamic range of our system, the energy of the emitted THz-wave was varied for 10 orders of magnitude using THz wave attenuators. At the frequency of 1.5 THz, we were able to achieve the dynamic range of about 100dB using commercially available near infrared photo detector. This system has potential applications in non-destructive sensing and imaging of a wide variety of materials.


    An injection-seeded terahertz parametric generator (is-TPG) is monochromatic with a widely tunable THz wave source and can obtain THz spectra directly over a relatively wide detection area. Therefore, the spectra from the contents contained in covering materials that refract, diffract, or scatter THz waves can be measured using is-TPG. Recent is-TPG research has resulted in a significant increase in power output and the highly sensitive detection of THz-waves. Studies have also developed a high dynamic range spectrometer using an is-TPG. In this study, in order to evaluate the performance of is-TPG in mail inspection, we measured the transmission spectra of various chemicals under different covering materials using an is-TPG spectrometer [1], and compared the spectra with those measured by THz-TDS.


[1]M. Kato, S. R. Tripathi, K. Murate, K. Imayama and K. Kawase, gNon-destructive drug inspection in covering materials using a terahertz spectral imaging system with injection-seeded terahertz parametric generation and detection,h Optics Express, 24(6), 6425-6432 (2016).

[2]K. Kawase, Y. Ogawa, Y. Watanabe, H. Inoue, gNon-destructive terahertz imaging of illicit drugs using spectral fingerprints,h Opt. Exp. 11 (2003) 2549.

[3K. Kawase, H. Minamide, K. Imai, J. Shikata, H. Ito,gInjection-seeded terahertz-wave parametric generator with wide tunability,h Appl. Phys. Lett. 80 (2002) 195.

[4]S. Hayashi, K. Nawata, T. Taira, J. Shikata, K. Kawase, H. Minamide, gUltrabright continuously tunable terahertz-wave generation at room temperature,h Sci. Rep. 4 (2014) 5045.

THz Spectropic Imaging of Illicit Drugs Hidden in an Envelope

Illicit drug samples
Spectroscopic imaging of illicit drugs
The Terahertz Tomography Three-Dimensional Image of three sheets of papers

"Professor Kodo Kawase" Electronics Letters, Vol. 46, No. 26, p. S65 (2010)

Kawase Laboratory,

Dept. of Electrical and Electronic Engineering and Information Engineering,
Graduate School of Engineering, Nagoya University, Furo-cho, Chikusa-ku, Nagoya, 464-8603 Japan

Phone +81 52 789 3169
Fax +81 52 789 4440

Professor Kodo Kawase
Mobile phone +81 90 9341 6334 Fax +81 52 789 4211
mail kawasenuee.nagoya-u.ac.jp

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