Takeshi Namioka’s research while affiliated with Tohoku University and other places

The present status is described of the vacuum ultraviolet/soft-X-ray spectroscopic facilities at the synchrotron radiation laboratories in Japan. An overview is presented of the spectroscopic instruments available and under development at the SOR-RING at the Institute for Solid State Physics, University of Tokyo, the Photon Factory-ring at the National Laboratory for High Energy Physics, the UVSOR at the Institute for Molecular Science, and the TERAS at the Electrotcchnical Laboratory. Emphasis is placed upon the unique features of the instruments developed in Japan.

A systematic study of the reproducibility of the VUV continuum emitted from a laser-produced samarium-plasma source driven by a 10-Hz Q-switched Nd: YAG laser is reported, and its possible use with a conventional scanning monochromator in absorption spectroscopy is demonstrated.

The principal series of helium has been observed up to n = 50 in the 10th order of a 6.65-m spectrograph with synchrotron radiation. The series limit 1s 2S is determined to be 198 310.75 ± 0.04cm−1, the error estimate being the standard deviation in the fitting procedure. The term values and effective quantum numbers are also given for the 1snp levels (4 n 50). It is confirmed that rotational lines of the CO 4th positive bands can serve as wavelength standards, even for a high-resolution spectrum.

The recent developments of VUV spectroscopic instruments are reviewed in connection with the advances in design methods and fabrication technology of optical elements. The design concepts and the performance of several grating instruments for use with synchrotron radiation, both normal incidence and grazing incidence, are discussed, with special emphasis on the high-resolution capability in the photoelectric detection mode.

The absorption spectrum of atomic Ca has been observed photographically in the wavelength region between 1410-1330 Å with the high-resolution spectrograph at the Photon Factory. Complex structures of the observed spectrum just below the 4p 2P1/2 threshold are found to be well reproduced by the recent ab-initio calculation done by Kim and Greene.

Reflectance degradation of soft X-ray reflection filters of Mo/Si and Rh/Si multilayers fabricated on SiC substrates was studied after exposure to Synchrotron Radiation for 26 and 140 hours, respectively. For both mirrors, darkening was seen at the exposed area, where peak reflectances around 100 eV photon energy were decreased from 45% to 35% in the Mo/Si and from 40% to 9.8% in the Rh/Si mirror. Unexposed areas retained much higher peak reflectances of over 30% in spite of the temperature increase of the substrates to over 110°C. At the exposed area of the Mo/Si mirror, a carbon layer was found and the attenuation factor in peak reflectance vs. photon energy was primarily explained by absorption in this layer.

The photoabsorption cross sections of Kr i in the photoionization threshold region [845-887 Å] have been measured with the highest resolving power (≥ 1.5 x 105) ever achieved in this wavelength region. The data obtained have been analyzed by means of least squares fitting with a line shape formula based on the multichannel quantum-defect theory. The quantum defects, width parameters, and asymmetry parameters thus determined are given together with the photoabsorption cross sections for the ns' and nd' series converging to the 2P1/2 ionization limit.

A soft X-ray reflectometer with a laser-produced plasma source driven by a Q-switched Nd: YAG laser or a XeCl excimer laser was constructed. By comparing the reflectances of a multilayer mirror with the data obtained using synchrotron radiation, its usefulness for reflectance measurements in the soft X-ray region (40-130 eV) is demonstrated.

The holographic plane grating with grooves of a radial form and its imaging properties in a converging beam are analyzed. The results are applied to the design of conical diffraction monochromators for the 1-4 keV region, and their expected performances are examined by means of ray tracing in comparison with the corresponding ruled radial grating. Design examples show that, in a conical diffraction monochromator covering the energy region of 1-4 keV, the holographic grating thus designed exhibits a resolving power equivalent to that of the ruled radial grating.

A new type of monochromators that incorporates two kinds of Monk-Gillieson monochromators has been designed and constructed for the purpose of realizing an evaluation beamline for characterizing soft X-ray optical elements in a wide wavelength range of 0.7-25 nm. One of the monochromators is a conventional type equipped with three varied-line-spacing plane gratings, allowing a choice of two inclusion angles. The other is a new type that employs a scanning mechanism based on Surface Normal Rotation (SNR). The SNR scheme provides high throughput at short wavelengths and simple scanning mechanism by means of a grating rotation about its normal. The monochromators is operated in the SNR and conventional modes over the ranges of 0.7-2.0 nm and 2.0-25 nm, respectively. The system was installed on a beamline of the AURORA, a superconducting compact storage ring, at the Synchrotron Radiation Center, Ritsumeikan University. In this paper we describe the optical and mechanical designs of the monochromators, and a practical method of wavelength calibration. Also experimental data are shown which demonstrate the performance and versatility of the new type of Monk-Gillieson monochromators.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.