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583 results on '"Kawase, Kodo"'

12. Noise-free terahertz-wave parametric generator

Author

Mine, Sota, Kawase, Kodo, Murate, Kosuke, Mine, Sota, Kawase, Kodo, and Murate, Kosuke

Abstract

We achieved noise-free terahertz (THz)-wave output from an injection-seeded THz-wave parametric generator (is-TPG) employing high-power injection seeding. A conventional is-TPG uses a weak continuous-wave (CW) seed beam. The position in which broadband noise is generated (via spontaneous parametric down-conversion) and the position of the THz signal overlap. Thus, the output features broadband TPG noise, reducing the signal-to-noise ratio. To solve this problem, we shifted the position in which the THz signal is generated to the front of the crystal; we separated the signal from broadband TPG noise using a high-powered, pulsed seed beam that was 107-fold more powerful than the CW seed beam. Thus, we extracted only the THz signal; we achieved a noise-free is-TPG. This system features a signal-to-noise ratio of 95 dB, approximately 40 dB better than the signal-to-noise ratio of the conventional system.

Published
2023

15. THz Tomography

Author

Shibuya, Takayuki, Kawase, Kodo, Peiponen, Kai-Erik, editor, Zeitler, Axel, editor, and Kuwata-Gonokami, Makoto, editor

Published
2013
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17. Terahertz Rays to Detect Drugs of Abuse

Author

Kawase, Kodo, Dobroiu, Adrian, Yamashita, Masatsugu, Sasaki, Yoshiaki, Otani, Chiko, Miles, Robert E., editor, Zhang, Xi-Cheng, editor, Eisele, Heribert, editor, and Krotkus, Arunas, editor

Published
2007
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22. Real-time wide dynamic range spectrometer using a rapidly wavelength-switchable terahertz parametric source

Author

Mine, Sota, Kawase, Kodo, Murate, Kosuke, Mine, Sota, Kawase, Kodo, and Murate, Kosuke

Abstract

In this study, we demonstrate real-time terahertz (THz) spectroscopy using a rapidly wavelength-switchable injection-seeded THz parametric generator. We developed a wavelength-switchable external cavity diode laser using a digital micromirror device as a seed source for the generator. We realized fast acquisition of THz spectra by switching the wavelength of the laser for each pump beam pulse. This system can rapidly switch wavelengths and easily increase the number of measurement wavelengths, and it also has a wide dynamic range, of more than 75 dB, and high stability. Furthermore, by combining this system with THz parametric detection, all wavelengths can be detected in a single frame using a near infrared camera for real-time reagent measurement.

Published
2022

43. Efficient Terahertz Parametric Source Using Flat Pump Beam

Author

Mine, Sota, Abe, Mitsuki, Kawase, Kodo, and Murate, Kosuke

Abstract

A flat pump beam was used to improve efficiency and miniaturize an injection-seeded terahertz-wave parametric generator (is-TPG). The improved power density of the pump beam and interaction length of the terahertz-wave reduced the required pump beam energy by > 85% compared with the conventional system. The reduced generation threshold made it possible to construct is-TPG spectroscopic systems with pump beams of ≤ 3 mJ.

Published
2023
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44. Tunability enhancement of a terahertz-wave parametric generator pumped by a microchip Nd:YAG laser

Author

Hayashi, Shin'ichiro, Shibuya, Takayuki, Sakai, Hiroshi, Taira, Takunori, Otani, Chiko, Ogawa, Yuichi, and Kawase, Kodo

Subjects
Nd-YAG lasers -- Design and construction, Nd-YAG lasers -- Properties, Nd-YAG lasers -- Equipment and supplies, Integrated circuits -- Usage, Integrated circuits -- Properties, Semiconductor chips -- Usage, Semiconductor chips -- Properties, Wave propagation -- Research, Nanotechnology -- Research, Standard IC, Astronomy, Physics
Abstract

We have enhanced the tunability of a terahertz-wave parametric generator using MgO:LiNb[O.sub.3] pumped by a subnanosecond, passively Q-switched, microchip Nd:YAG laser. This pump source allows high-intensity pumping without damage to the nonlinear crystal and generates a narrow linewidth and tunable terahertz wave with injection seeding by an external cavity diode laser for the idler wave. The high-intensity pumping causes a gain curve broadening of the terahertz-wave parametric generation, especially in the high-frequency region. We obtained an output terahertz wave with a tuning range of 0.9-3 THz (100-330 [micro]m), a peak power of 100 mW, and a linewidth of less than 10 GHz. This room temperature operated, palm-sized source promises to be a widely tunable terahertz-wave source that is suited to a variety of applications. OCIS codes: 140.3070, 190.2620, 190.4360, 190.4410, 190.4970.

Published
2009

49. Output power enhancement of a palmtop terahertz-wave parametric generator

Author

Hayashi, Shin'ichiro, Minamide, Hiroaki, Ikari, Tomofumi, Ogawa, Yuichi, Shikata, Jun-ichi, Ito, Hiromasa, Otani, Chiko, and Kawase, Kodo

Subjects
Terahertz radiation -- Analysis, Laser speckle -- Analysis, Astronomy, Physics
Abstract

Broadband terahertz (THz) waves were generated by optical parametric processes based on laser light scattering from the polariton mode of a nonlinear crystal. By using the parametric oscillation of a MgO-doped LiNb[O.sub.3] crystal pumped by a nanosecond Q-switched Nd:YAG laser, we have realized a broadband, high-energy and compact THz-wave source. We report the development of a THz-wave parametric generator (TPG) using a small pump source with a short pulse width and a top-hat beam profile. These characteristics of the pump beam permit high-intensity pumping especially close to the output surface of the THz wave without thermal damage to the crystal surface. We also calculated the outcoupled THz wave for beams with two different intensity profiles: a top-hat beam (in this experiment) and a Gaussian beam (previously reported). The result shows the mechanism of the output energy and/or power enhancement. OCIS codes: 190.0190, 140.3070, 190.4410, 190.4970.

Published
2007

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