Mikihiko Ikezawa

Luminescencs of Alkali Halide Crystals Induced by UV-Light at Low Temperature

The luminescence of pure alkali halide crystals induced by the excitation with UV-light in the fundamental absorption region at low temperature is observed in NaCl, KCl, RbCl, NaBr, KBr, RbBr and KI. In KCl, RbCl and NaBr one emission band, in NaCl, KBr and RbBr two emission bands and in KI three emission bands are induced at 11°K. All of the emission bands, except one in KI, are confirmed to arise from the self-trapped exciton, or the V k - center. The quantum efficiencies for the luminescence are estimated as small as 0.1 to 0.2 in KCl, KBr and RbCl and a little larger in the other crystals. The excitation spectra and temperature dependence of the intensity of the luminescence are measured and the results are discussed in connection with the properties of the V k - center.

Optical Study on Electronic Structure of Rare-Earth Sesquioxides.

Reflectivity spectra of nine rare-earth sesquioxide ( R 2 O 3 ; R = La, Pr, Nd, Sm, Eu, Er, Tm, Yb and Lu) single crystals have been measured in the photon energy range from 0.5 to 50 eV at 300 K. The fundamental optical absorption has been clarified in connection with the electronic structure of R 2 O 3 . The absorption due to an intra-atomic optical transition of R 4 f → R 5 d 6 s was observed in the same energy region as the charge transfer excitation of O 2 p → R 5 d 6 s in the energy range of 6–15 eV. The absorption structure of the R 4 f → R 5 d 6 s transition and the R 5 p → R 5 d 6 s transition are explained by using the crystal field splitting of the 5 d band and the multiplet structure of the 4 f n -1 final state in photoemission process. Fine structures due to the absorption of the R 4 f → O 3 s transition in the energy region of the O 2 p → O 3 s absorption were observed and also can be explained by the 4 f n -1 final state.

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...

Reflectivity and Electronic Structures of Layered Ionic Crystals, (CnH2n+1NH3)2CdCl4: n=1, 2, 3

The reflection spectra of (C n H 2 n +1 NH 3 ) 2 CdCl 4 were measured in the photon energy region of 0.5–25 eV at room temperature (RT) and liquid nitrogen temperature (LNT) by means of synchrotron radiation. It was found that absorption spectra of the present crystals resemble that of CdCl 2 crystals except for an additional peak at 5.10 eV (RT). The energy of the additional peak shifts with temperature by as much as 0.38 eV from 5.10 eV (RT) to 5.48 eV (LNT). This absorption peak has doublet structure and the splitting energy is 0.1 eV, which is the same magnitude as the spinorbit splitting of a chlorine atom. The band is assigned to be an electronic transition from the chlorine 3 p valence band to a new-type conduction band which is composed of alkylammonium bases and is below the ordinary Cd 5 s conduction band in energy.

Temporary Bleaching of the M Band in KBr ana KCl

Temporary bleaching of color centers in additively colored KBr and KCl crystals are investigated. The first and the second absorption bands of M center are bleached by F -light or M -light irradiation at 90°K. Accompanying with the bleaching of the M band, two absorption bands grow at 555 mµ and 780 mµ in KBr and at 505 mµ and 690 mµ in KCl. These bands as well as the bleached M bands show dichroism when the original M band is dichroic. The oscillator strengths of these bands are determined with respect to the M band, and discussions on the nature of the bands are made.

Feasibility of optical diffraction radiation for a non-invasive low-emittance beam diagnostics

Abstract A “proof-of-principle” experiment on the optical diffraction radiation (ODR) as a single-pulse beam profile monitor is planned using an electron beam extracted from the KEK-ATF damping ring. The main goals of this experiment are the following: (i) To measure the yield and the angular distributions of the optical diffraction radiation from a large-size target at different wavelengths, impact parameters and beam characteristics for a comparison with analogous characteristics of optical transition radiation from a foil with identical optical parameters and for a verification of the model assumption (perfectly conducting semi-infinite target). (ii) To investigate the ODR angular distributions from a tilted target with a slit for observing the interference effects. (iii) To compare the results obtained by simulations based on classical approaches, taking into account the optical characteristics of the equipment and the beam parameters. (iv) To estimate the prospects of using ODR as a new non-invasive tool for ultrarelativistic beams. We estimated that the ODR photon yield in 10% bandwidth for 500 nm is about 106 photons/bunch with an impact parameter of 100 μm . This indicates that the ODR monitor is a promising candidate for single-pulse beam-profile measurements, and that it will be an extremely useful instrument for future linear colliders (JLC, NLC, TESLA and CLIC).

Far-infrared spectroscopy by synchrotron radiation at the UVSOR Facility

At the UVSOR Facility, Institute for Molecular Science, the practical use of the synchrotron radiation as a far-infrared light source has started. A spectroscopic system has been constructed at the beam line BL6A1 of UVSOR storage ring, which covers the wavenumber region from 5 to 250 cm−1. The cross sectional diameter of the light beam at the sample position is as small as 3 mm with the angular divergence of about 100 mrad. The system has been made mainly for the transmission and reflection measurements of small samples with small angular divergence by the use of the high brightness of the synchrotron radiation. Examples of observed transmission and reflectivity spectra are shown.

Optical Reflectivity of Single Crystals of YBa2Cu3O7-δ and ErBa2Cu3O7-δ

Optical reflectivity in the ab-plane of single crystals of YBa2Cu3O7-δ and ErBa2Cu3O7-δ has been observed at room temperature in the energy region from 0.5 to 5.6 eV. The reflectivity is isotropic in the ab-plane around the Drude edge at 1.5 eV. In the low-energy region below the edge, it is explained well by the Drude formula for the free carriers with an extremely short relaxation time of about 4×10-16 s.

Mixed valence of praseodymium oxides

Abstract Reflectivity and resonant photoemission spectra of three kinds of Pr-oxide single crystals were measured to investigate the valence of the Pr-ion in Pr-oxides. The coexistence of the valence states of Pr 3+ and Pr 4+ in PrO 2 −δ was observed.

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.