Toshiharu Takahashi

Kyoto University, Kioto, Kyōto, Japan

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Publications (30)45.13 Total impact

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    ABSTRACT: We report the design of a THz beamline for coherent synchrotron radiation (CSR) at the UVSOR-III very-low-emittance synchrotron radiation light source. The emitted THz-CSR is collected by a three-dimensional "magic mirror," which is a perfect collecting mirror for bending-magnet radiation with an acceptance angle of 288 mrad (H) × 80 mrad (V). A quasi-monochromatic THz-CSR with an average flux of 104 μW/0.1 % b.w. and a peak power of 120 nJ/pulse/0.1 % b.w. is expected at the beamline.
    Journal of Physics Conference Series 05/2012; 359(1). DOI:10.1088/1742-6596/359/1/012009
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    ABSTRACT: At UVSOR-II, Institute for Molecular Science, a new beamline for novel pump-and-probe spectroscopy experiments combining terahertz (THz) coherent synchrotron radiation and vacuum-ultraviolet coherent harmonic generation from same electron bunches in the storage ring interacted with an amplitude-modulated pulse laser introduced from the outside of the storage ring. The purpose of the beamline is to elucidate the electronic structure relating to physical properties of solids by using selective excitations of low energy electronic and vibrational structure. The beamline design is reported.
    06/2010; DOI:10.1063/1.3463287
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    ABSTRACT: We have observed the spatial inhomogeneity of the electronic structure of a single-crystalline electron-doped EuO thin film with ferromagnetic ordering by employing infrared magneto-optical imaging with synchrotron radiation. The uniform paramagnetic electronic structure changes to a uniform ferromagnetic structure via an inhomogeneous state with decreasing temperature and increasing magnetic field slightly above the ordering temperature. One possibility of the origin of the inhomogeneity is the appearance of magnetic polaron states.
    Physical review. B, Condensed matter 10/2008; 78(5). DOI:10.1103/PhysRevB.78.052409 · 3.66 Impact Factor
  • Toshiharu Takahashi, Kiyoshi Takami
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    ABSTRACT: A single-bunch beam has been generated using a developed high-speed avalanche-type pulser in KURRI-LINAC in order to lift restrictions of the spectral resolution in the spectroscopic study and the delay time in the time-resolved measurement. Both of the rise and fall times of the developed pulser are 110 ps. The observation of CTR has confirmed the single-bunch beam. The degree of impurity of single bunch has been estimated to be 1.5% by the analysis of the interferogram. (c) 2007 Elsevier B.V. All rights reserved.
    Infrared Physics & Technology 05/2008; DOI:10.1016/j.infrared.2007.12.029 · 1.46 Impact Factor
  • Shuichi Okuda, Toshiharu Takahashi
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    ABSTRACT: The characteristics and applicability of the absorption spectroscopy system using the coherent transition radiation light source have been investigated. The configurations of the system are relatively simple. The operational conditions of an electron linear accelerator have been evaluated. The stability of the light intensity has been within ±2–3% in a wavenumber range of 4–13 cm−1. The light intensity has been found to be more than six orders of magnitude higher than that for the lowest limit for detection.
    Infrared Physics & Technology 05/2008; DOI:10.1016/j.infrared.2007.12.015 · 1.46 Impact Factor
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    ABSTRACT: A laser bunch slicing system has been constructed at the UVSOR-II electron storage ring to produce a submillimeter-sized microstructure on an electron bunch. As its first result, terahertz coherent synchrotron radiation (THz CSR) was successfully produced by the dense structure of the electron bunch. Its intensity is higher by four or five orders of magnitude than that of normal synchrotron radiation. The intensity is proportional to the square of the peak current of the electron bunch, as expected for coherent emission. It is also demonstrated that the spectral shape of the THz CSR can be controlled by changing the slicing laser pulse duration.
    Japanese Journal of Applied Physics 12/2007; 46(12):7939-. DOI:10.1143/JJAP.46.7939 · 1.06 Impact Factor
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    ABSTRACT: The fluctuation of the electron bunch duration due to energy spectrum instability in a laser plasma cathode has been examined. Previous experiments clearly proved that a laser plasma cathode can generate ultrashort electron bunches with a bunch duration of 130fs (FWHM) and a geometrical emittance 0.07πmmmrad. The effect of temporal elongation of electron bunches due to their energy spread is estimated and the results are in good agreement with previous experiments. It is also clarified that the instability of the energy spectrum not only leads to a fluctuation of the bunch shape but also to a time-of-flight jitter, affecting possible future applications of a laser plasma cathode.
    Nuclear Instruments and Methods in Physics Research Section B Beam Interactions with Materials and Atoms 08/2007; 261(1):5-8. DOI:10.1016/j.nimb.2007.04.081 · 1.19 Impact Factor
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    ABSTRACT: Development of intense terahertz radiation source is progressing at UVSOR-II, based on the mechanism of coherent synchrotron radiation (CSR). The terahertz CSR has successfully been produced by two methods. When the storage ring is operated in the single bunch mode with a sufficiently high beam current, intense bursts of terahertz radiation are emitted. Micro-structures in the longitudinal density distribution of the electron bunches created by a beam instability may be the origin of the radiation. The duration of the bursts is typically 100 micro-seconds. The peak intensity is 10000 times higher than that of the normal synchrotron radiation. The bursts appear chaotically or quasi-periodically depending on the beam current with a typical interval of 10 milli-seconds. It has been also demonstrated that the terahertz CSR could be produced by the laser-bunch slicing method. The density modulation produced on the electron bunch by the laser is the origin of CSR. The repetition rate of the terahertz pulses is 1 kHz, which is same as the laser repetition rate. The intensity per pulse is 105 times higher than that of the normal SR.
    01/2007; DOI:10.1063/1.2436008
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    ABSTRACT: The magnetic field-induced superconductor-insulator-metal transition (SIMT) in partially deuterated $\kappa$-(BEDT-TTF)$_2$Cu[N(CN)$_2$]Br, which is just on the Mott boundary, has been observed using the infrared magneto-optical imaging spectroscopy. The infrared reflectivity image on the sample surface revealed that the metallic (or superconducting) and insulating phases coexist and they have different magnetic field dependences. One of the magnetic field dependence is SIMT that appeared on part of the sample surface. The SIMT was concluded to originate from the balance of the inhomogenity in the sample itself and the disorder of the ethylene end groups resulting from fast cooling. Comment: 5 pages, 5 figures, to appear in Phys. Rev. B
    Physical review. B, Condensed matter 12/2006; 75(1). DOI:10.1103/PhysRevB.75.014525 · 3.66 Impact Factor
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    ABSTRACT: The characteristics of the far-infrared light source using the coherent radiation emitted from a high-energy short electron bunch have been investigated. The coherent radiation has a continuous spectrum in a submillimeter to millimeter wavelength range and the brightness is relatively high. The spectrum of the radiation is determined by the longitudinal form factor of the electron bunch. The operational conditions of a high-current linear accelerator have been optimized using an electron bunch shape monitor. The coherent transition radiation light source has been applied to absorption spectroscopy for liquid water and to an imaging experiment for a leaf of rose.
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    ABSTRACT: Recently, several plasma cathodes at universities and institutes can generate a monoenergetic electron beam. LBL measured the bunch length by the CTR (Coherent Transition Radiation) interferometer to determine it as about 50 fs (FWHM). We are trying to carry out a single-shot measurement of the bunch length by a infrared polychromator. As the first step forward it, we measured the CTR spectra emitted at a 300microm-thick Ti foil by the electron beams from our plasma cathode. The laser parameters are 12 TW, 50fs, 3×1019W/cm2. He gas-jet is used and the electron density is 6×1019cm-3. By using the liquid He bolometer and several optical low-pass filter, we measured the spectra of the CTR. We can clearly classify the difference of the spectrum and bunch length for the monoenergetic and Maxwellian beams. The numerical analysis of the bunch elongation due to the energy spread confirms the experimental results. The bunch length of the monoenergetic beam is less than 100 fs at FWHM with about 10 pC per bunch, which is consistent with the PIC simulation. The next single-shot measurement with the FIR (Far-Ingfra-Red) polychomator and application to a pump-and-probe experiment for radiation chemsitry are also discussed.
    01/2006; DOI:10.1063/1.2409218
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    ABSTRACT: We have detected very intense bursts of terahertz synchrotron radiation at the UVSOR-II electron storage ring operated in single bunch mode. The bursts were observed in the wavelength range from 0.2 to 3.0 mm by using a liquid-helium-cooled InSb hot-electron bolometer. The typical duration and interval of the bursts were about 200 μs and 10-15 ms, respectively. Each burst shows the quasi-periodic structure of about 30 μs. The peak intensity of the bursts was about 10000 times larger than that of ordinary synchrotron radiation in the same wavelength region. The extremely high intensity strongly suggests that the bursts are coherent synchrotron radiation, although the radiation wavelength was much shorter than the electron bunch length.
    Japanese Journal of Applied Physics 07/2005; 44(33-36):L1131-L1133. DOI:10.1143/JJAP.44.L1131 · 1.06 Impact Factor
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    ABSTRACT: A short-bunched beam of electrons of an L-band linac of 38MeV is guided to a cylindrical-closed resonator. Wavepackets of coherent transition radiation (CTR) generated from bunches passing through the mirrors are coherently summed up in the resonator. The amplification of the output of the resonator is confirmed in comparison with spontaneous CTR. The temporal structure of the output, observed with a hot-electron bolometer having the response time of 0.35μs, shows oscillating characteristic of about 1μs in time scale. The result strongly suggests the inter-bunch distance varies rapidly over the duration of a macropulse, and it consequently results in degradation of the coherent summing up in the resonator.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 08/2004; DOI:10.1016/j.nima.2004.04.037 · 1.32 Impact Factor
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    ABSTRACT: Using a short-bunched beam of electrons of a linear accelerator, the electromagnetic impulses of coherent transition radiation (CTR) are superposed on the subsequent impulses coherently. The output of a closed resonator is compared with spontaneous CTR to verify amplification of radiation. The main cavity mode is assigned to be TM02 from observation of the radial distribution of the intensity. Experiment on the influence of the size of the resonator shows that the output intensity increases with the volume of the resonator.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 08/2004; DOI:10.1016/j.nima.2004.04.038 · 1.32 Impact Factor
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    ABSTRACT: We constructed a magneto-optical microspectroscopy apparatus in the infrared region using a synchrotron radiation, SPring-8. In the apparatus, an infrared microscope with the spatial resolution of is combined with low temperatures and high magnetic fields . The purpose is to investigate the electronic structure under extreme conditions of tiny materials such as organic conductors and of small region and the spatial distribution of electronic structures. After the installation of high pressure cells, optical measurements under multiple-extreme conditions is available. The specification of the apparatus and recent results of an organic superconductor are presented.
    Physica B Condensed Matter 05/2003; DOI:10.1016/S0921-4526(02)02431-6 · 1.28 Impact Factor
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    ABSTRACT: The bunch shape of single-bunch electron beams, generated with a 38 MeV L-band linear accelerator, was evaluated using the longitudinal bunch form factor at the Institute of Scientific and Industrial Research at Osaka University. The single-bunch beams are being used in experiments for generating self-amplified spontaneous emission and coherent radiation. In the present experiments, the energy of the electron beam was 27 MeV, the energy spread 1.1% FWHM, and the electron charge in a bunch 13.5 nC. The form factor was obtained from the spectrum of the coherent transition radiation measured with a Martin–Pupplet interferometer. A streak measurement was also performed in the same configurations and the results were compared to those for the measurements of the coherent radiation. By using these two methods, the performance of a chicane-type bunch compressor was investigated.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 12/2001; 475(1-3):478-491. DOI:10.1016/S0168-9002(01)01606-0 · 1.32 Impact Factor
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    ABSTRACT: Circularly polarized light was generated in the millimeter wavelength region from superposition of forward transition radiation (TR) and backward TR emitted from two metallic screens placed along a trajectory of a short-bunch beam of electrons of 42 MeV. The degree of the circular polarization was analyzed to be 97% of the polarized radiation at λ = 2.25 mm, using a Soleil’s compensator and a wire-grid polarizer. The geometry of the metallic screens was discussed from the point of the phase difference between the forward TR and the backward TR. © 2001 American Institute of Physics.
    Review of Scientific Instruments 07/2001; 72(8):3221-3224. DOI:10.1063/1.1387255 · 1.58 Impact Factor
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    ABSTRACT: Short bunches of 150-MeV electrons of a linear accelerator passed along the surface of a crystal quartz or a teflon and coherent Cerenkov radiation from the solid dielectrics has been observed in the wavelength range from 0.5 to 4 mm. Properties of the radiation have been experimentally investigated. The angular distribution of the observed radiation showed a maximum peak in the direction of the Cerenkov angle with several satellite peaks. The intensity increased linearly with increasing the length of the medium and was proportional to the square of the number of electrons in the bunch. The spectral intensity was enhanced by almost five orders of magnitude in comparison with the theoretical calculation of incoherent radiation.
    Physical review. E, Statistical physics, plasmas, fluids, and related interdisciplinary topics 01/2001; 62(6 Pt B):8606-11. DOI:10.1103/PhysRevE.62.8606 · 2.33 Impact Factor
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    ABSTRACT: The coherent synchrotron radiation has a continuous spectrum in a submillimeter to millimeter range and is highly intense compared with the other far-infrared light sources. A new light source was established by using the coherent radiation from the intense single-bunch electron beam generated with the 38 MeV L-band linear accelerator at The Institute of Scientific and Industrial Research, Osaka University. In the experiments the beams at an energy of 27 MeV and a charge of electrons in a bunch of 30 nC were used. The intensity, stability and polarization of the coherent synchrotron radiation were measured at wavelengths of 0.7–1.4 mm. The absorption spectroscopy was carried out for gas. The results agreed with those obtained by calculation. The application of the pulsed radiation which is synchronized with the electron bunch, to stroboscopic pulse-radiolysis experiments is under preparation.
    Nuclear Instruments and Methods in Physics Research Section A Accelerators Spectrometers Detectors and Associated Equipment 05/2000; 445(1-3):267-271. DOI:10.1016/S0168-9002(00)00081-4 · 1.32 Impact Factor
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    ABSTRACT: A spectroscopic system for the millimeter-wave region has been constructed on the coherent radiation beamline at the KURRI-LINAC of the research reactor institute, Kyoto University. Coherent transition radiation has been used as the light source. The observed spectrum of radiation was distributed throughout the entire millimeter-wave region and the intensity was four orders of magnitude larger than that of the conventional light source which has the continuous spectrum, i.e., a mercury-arc lamp. The interference between wave packets emitted from successive bunches was observed. It showed that the spectrum of coherent transition radiation was constituted of the higher harmonics of the L-band radio frequency (1.3 GHz) and that the high resolution spectrum was not a continuous spectrum. The diameter of the light beam at the position of a sample was about 9 mm (full width half maximum) and it increased as the wavelength became long because of the diffraction effect for the finite sizes of the optical components. Using the spectroscopic system, the pure rotational spectrum of N2O gas was observed in the millimeter-wave region. © 1998 American Institute of Physics.
    Review of Scientific Instruments 10/1998; 69(11):3770-3775. DOI:10.1063/1.1149177 · 1.58 Impact Factor