Kimihiro Ishi

Reversible photoinduced spectral change in Eu2O3 at room temperature

When Eu2O3 powder compact and film are irradiated with ultraviolet (UV) laser light in a vacuum, their photoluminescence (PL) spectra change from a red sharp-line structure to a white broad band, which can be clearly seen with the naked eye. After removing the UV laser light, the white PL continues for more than several months at room temperature under room light, in spite of any changes of atmosphere. By irradiating with the same UV laser light at room temperature under O2 gas atmosphere, the original red PL state reappears. Such a reversible phenomenon may well yield materials for white-light-emitting devices and erasable optical storage.

Utilization of coherent transition radiation from a linear accelerator as a source of millimeter-wave spectroscopy

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 componen...

Far infrared spectrum of crystalline carbon disulphide

Abstract The far infrared spectrum of crystalline carbon disulphide has been measured at about 1.8 K. Two absorption bands are observed, with maxima at 66.5 and 68.2 cm −1 , respectively, and with nearly equal intensities. They are considered to be due to the two infrared active translational modes expected by lattice dynamics.

Femtosecond electron beam generation and measurement for laser synchrotron radiation

One of the S-band twin linacs (18L linac) of Nuclear Engineering Research Laboratory of University of Tokyo is modified in order to produce femtosecond electron single bunch for femtosecond X-ray generation via Thomson backward scattering, namely laser synchrotron radiation. Laser photocathode RF gun and chicane-type magnetic pulse compressor are installed at the S-band linac. 10 ps (FWHM) laser pulse generates 5 MeV, 10 ps (FWHM), 1 nC electron single bunch, which is accelerated up to 20 MeV in the S-band accelerating tube and compressed to 200 fs (FWHM) by the chicane. Design study has been performed by using the code of PARMELA and the installation has been finished. For precise and reliable measurement of the compressed pulse length, the comparison of measurement between the femtosecond streak camera and coherent transition radiation interferometry was carried out. Good agreement between them for 1—10 ps (FWHM) pulses was achieved. A new Michelson interferometer for the 200 fs pulse is now under construction. ( 1998 Elsevier Science B.V. All rights reserved.

Coherent synchrotron radiation at submillimeter and millimeter wavelengths

Abstract To study the coherence effect of synchrotron radiation (SR), light emission from the Tohoku 300 MeV linac, whose energy and bunch length of electrons were 180 MeV and a few millimeters, was observed in the submillimeter and millimeter wavelength regions by using a grating spectrometer. The absolute intensity of ordinary SR in the visible region was also measured. In comparison with ordinary SR, the absolute intensity of SR in the millimeter wavelength region was enhanced by about a factor of 10 6 , which corresponded roughly to the number of electrons in one bunch. The intensity of enhanced SR showed the quadratic dependence on the beam current. The enhanced SR was strongly polarized in the electron orbital plane. The relation between the electron distribution in a bunch and the spectra of coherent SR is discussed.

Prebunched free electron laser with a broadband spectrum

Abstract The wave packets of coherent synchrotron radiation emitted from a short-bunch beam of electrons of a linear accelerator are stored in an optical resonator to stimulate the radiation from the successive bunches. The output of the resonator has a broad spectrum composed of the higher harmonics of the RF of the linac in the millimeter and submillimeter wave region.

Exotic radiation from a photonic crystal excited by an ultrarelativistic electron beam.

We report the observation of an exotic radiation (unconventional Smith-Purcell radiation) from a one-dimensional photonic crystal. The physical origin of the exotic radiation is direct excitation of the photonic bands by an ultra-relativistic electron beam. The spectrum of the exotic radiation follows photonic bands of a certain parity, in striking contrast to the conventional Smith-Purcell radiation, which shows solely a linear dispersion. Key ingredients for the observation are the facts that the electron beam is in an ultra-relativistic region and that the photonic crystal is finite. The origin of the radiation was identified by comparison of experimental and theoretical results.

A prebunched FEL based on coherent transition radiation in the far-infrared region

Abstract A short-bunch beam of electrons of 150 MeV is led to an open resonator of semi-confocal type. The wavepackets of coherent transition radiation (TR), emitted from bunched electrons passing through mirrors of the resonator, go back and forth in the resonator and superpose on the subsequent bunches to stimulate coherent TR. The main mode is assigned as TEM 01 , and the intensity depends on the square of the beam current. The output intensity of the resonator is compared with the coherent spontaneous TR generated within the resonator to show amplification of radiation due to the stimulated emission.

Temperature dependence of the infrared active translational modes of solid carbon disulphide

Two infrared active translational modes of solid CS2, B1u(Γ−3) and B2u(Γ−2) were precisely measured from the temperature of liquid helium to the melting point. Remarkable temperature dependencies of the absorption bandwidths were obtained and explained by means of the perturbation theory of the anharmonic crystal. The results suggest ways in which the lattice vibration energy is dissipated or transferred.

Suppression of coherent synchrotron radiation in conducting boundaries

The intensity of coherent synchrotron radiation was measured in the presence of finite parallel plate metallic shields with a variable gap by using the Tohoku 300 MeV Linac. The results can be qualitatively explained by the theory of suppression effect obtained by Nodvick and Saxon.<<ETX>>