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Your search keyword '"Yokoyama, Shuko"' showing total 47 results
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47 results on '"Yokoyama, Shuko"'

1. Super-resolution discrete-Fourier-transform spectroscopy using precisely periodic radiation beyond time window size limitation

Author

Yasui, Takeshi, Iyonaga, Yuki, Hsieh, Yi-Da, Sakaguchi, Yoshiyuki, Hindle, Francis, Yokoyama, Shuko, Araki, Tsutomu, and Hashimoto, Mamoru

Subjects
Physics - Optics
Abstract

Fourier transform spectroscopy (FTS) has been widely used in a variety of fields in research, industry, and medicine due to its high signal-to-noise ratio, simultaneous acquisition of signals in a broad spectrum, and versatility for different radiation sources. Further improvement of the spectroscopic performance will widen its scope of applications. Here, we demonstrate improved spectral resolution by overcoming the time window limitation using discrete Fourier transform spectroscopy (dFTS) with precisely periodic pulsed terahertz (THz) radiation. Since infinitesimal resolution can be achieved at periodically discrete frequencies when the time window size is exactly matched to the repetition period T, a combination of THz-dFTS with a spectral interleaving technique achieves a spectral resolution only limited by the spectral interleaving interval. Linewidths narrower than 1/(50T) are fully resolved allowing the attribution of rotational-transition absorption lines of low-pressure molecular gases within a 1.25 MHz band. The proposed method represents a powerful tool to improve spectrometer performance and accelerate the practical use of various types of FTS., Comment: 26 pages, 5 figures

Published
2014
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2. Gapless dual-comb spectroscopy in terahertz region

Author

Yasui, Takeshi, Hsieh, Yi-Da, Iyonaga, Yuki, Sakaguchi, Yoshiyuki, Yokoyama, Shuko, Inaba, Hajime, Minoshima, Kaoru, Hindle, Francis, and Araki, Tsutomu

Subjects
Physics - Optics
Abstract

We demonstrated combination of gapless terahertz (THz) comb with dual-comb spectroscopy, namely gapless dual-THz-comb spectroscopy, to achieve the spectral resolution equal to width of the THz comb tooth. The gapless THz comb was realized by interpolating frequency gaps between the comb teeth with sweeping of a laser mode-locked frequency. The demonstration of low-pressure gas spectroscopy with gapless dual-THz-comb spectroscopy clearly indicated that the spectral resolution was decreased down to 2.5-MHz width of the comb tooth and the spectral accuracy was enhanced to 10-6 within the spectral range of 1THz. The proposed method will be a powerful tool to simultaneously achieve high resolution, high accuracy, and broad spectral coverage in THz spectroscopy., Comment: 12 pages, 4 figures

Published
2013
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4. Absolute distance measurement of optically rough objects using asynchronous-optical-sampling terahertz impulse ranging

Author

Yasui, Takeshi, Kabetani, Yasuhiro, Ohgi, Yoshiyuki, Yokoyama, Shuko, and Araki, Tsutomu

Subjects
Terahertz radiation -- Usage, Time-of-flight mass spectrometry -- Methods, Distances -- Measurement, Distances -- Methods, Distances -- Technology application, Technology application, Astronomy, Physics
Abstract

We report on a real-time terahertz (THz) impulse ranging (IPR) system based on a combination of time-of-flight measurement of pulsed THz radiation and the asynchronous-optical-sampling (ASOPS) technique. The insensitivity of THz radiation to optical scattering enables the detection of various objects having optically rough surfaces. The temporal magnification capability unique to ASOPS achieves precise distance measurements of a stationary target at an accuracy of -551 [micro]m and a resolution of 113 [micro]m. Furthermore, ASOPS THz IPR is effectively applied to real-time distance measurements of a moving target at a scan rate of 10 Hz. Finally, we demonstrate the application of ASOPS THz IPR to a shape measurement of an optically rough surface and a thickness measurement of a paint film, showing the promise of further expanding the application scope of ASOPS THz IPR. The reported method will become a powerful tool for nondestructive inspection of large-scale structures. OCIS codes: 110.6795, 120.0280, 280.3400, 280.5600.

Published
2010

6. Intermode beat stabilized laser with frequency pulling

Author

Yokoyama, Shuko, Araki, Tsutomu, and Suzuki, Norihito

Subjects
Lasers -- Research, Astronomy, Physics
Abstract

A frequency-stabilized two-mode He-Ne laser has been developed. The intermode beat frequency of the experimental laser was approximately 600 MHz for a 25-cm cavity. The laser frequency in which the mode stands is pulled to the center of the gain curve (frequency pulling). The degree of pulling depends on where the longitudinal modes stand in the broadened gain curve. Beat frequency is thereby changed periodically of the order of hundreds of kilohertz with respect to cavity expansion. The frequency pulling was effectively used for frequency stabilization of the laser. The standing position of the longitudinal mode lights was locked in the gain curve by controlling the change of intermode beat frequency. A microwave mixer was applied to extract the frequency change of the intermode beat. Excellent frequency stability (10 to the tenth power for the laser oscillation and 10 to the sixth power for the beat frequency) was attained. The polarization orthogonality of the proposed laser was superior to that of Zeeman lasers.

Published
1994

13. Terahertz Comb Spectroscopy Traceable to Microwave Frequency Standard

Author

Hsieh, Yi-Da, primary, Iyonaga, Yuki, additional, Sakaguchi, Yoshiyuki, additional, Yokoyama, Shuko, additional, Inaba, Hajime, additional, Minoshima, Kaoru, additional, Hindle, Francis, additional, Takahashi, Yoshinori, additional, Yoshimura, Masashi, additional, Mori, Yusuke, additional, Araki, Tsutomu, additional, and Yasui, Takeshi, additional

Published
2013
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14. Gapless THz Comb Spectroscopy

Author

Yasui, Takeshi, primary, Hsieh, Yi-Da, additional, Iyonaga, Yuki, additional, Sakaguchi, Yoshiyuki, additional, Yokoyama, Shuko, additional, Inaba, Hajime, additional, Minoshima, Kaoru, additional, and Araki, Tsutomu, additional

Published
2013
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16. Sub-nanometre Double Shearing Heterodyne Interferometry for Profiling Large Scale Planar Surfaces

Author

Yokoyama, Toshiyuki, Yokoyama, Shuko, Yoshimori, Kyu, Araki, Tsutomu, Yokoyama, Toshiyuki, Yokoyama, Shuko, Yoshimori, Kyu, and Araki, Tsutomu

Abstract

A novel interferometric method, called a double shearing interferometry, is presented for profiling large-scale quasi-planar surfaces, such as semiconductor wafers, optical flats and x-ray mirrors. The surface profile is measured even under existence of the inclination of a scanning stage. By adopting the common-path optical configuration and the heterodyne detection, the proposed method realizes excellent resolution in sub-nanometer order and enables a robust measurement against unwanted disturbances due to the measurement environments. A height resolution of 0.1nm was experimentally achieved. A standard deviation of the analytical surface profiles was found to be 1.3nm, even when using a conventional screw-lead scanning stage. The measured results show that the surface profile and stage inclination are separately determined. We confirmed resultant profile was well consistent with the one measured with Fizeau interferometer.

Published
2004

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