T. Shidara

Elliptical-polarization analyses of synchrotron radiation in the 5–80-eV region with a reflection polarimeter

Abstract The Stokes parameters, which completely represent the polarization state of light, have been measured in the 5–80-eV energy region for synchrotron-radiation beams on the VUV to soft X-ray beamlines at the Photon Factory. Various states of polarization were produced for the emerging beam by deflecting the incoming beam vertically with respect to the entrance slit of the monochromator with a premirror of the beamline. The resultant beam was polarization-analyzed using a polarimeter comprising two triple-reflection polarizers. Increasing the beam-deflection angle was found to result in a change in the polarization state from predominantly horizontal linear polarization to elliptical polarization. This procedure could be used both to produce and to verify circular polarization with | P c | ≳ 80% in the energy range 60–80 eV, which could be immediately applied to MCD experiments. Unpolarized light could clearly be distinguished from circularly polarized light. The unpolarized component was found to become larger with increasing energy on a soft X-ray beamline; this was shown to be mainly due to scattering by beamline optical elements.

The KEKB injector linac

Abstract An 8-GeV electron/3.5-GeV positron injector for KEKB was completed in 1998 by upgrading the existing 2.5-GeV electron/positron linac. The main goals were to upgrade its accelerating energy from 2.5 to 8 GeV and to increase the positron intensity by about 20 times. This article describes not only the composition and features of the upgraded linac, but also how these goals were achieved, by focusing on an optics design and commissioning issues concerning especially high-intensity single-bunch acceleration to produce positron beams.

Investigation of carbon contamination of synchrotron radiation mirrors

Abstract Carbon-contaminated synchrotron radiation mirrors have been successfully cleaned by a dc glow discharge in oxygen. Reflectance and angle-resolved scattering have been measured before and after cleaning. The effect of carbon contamination on reflectance is severe at near normal incidence whereas it is small at grazing incidence. The decrease in reflectance is most noticeable for photons with an energy below about 10 eV. In the discharge arrangement in which the mirror surface did not face an electrode, the reflectance of contaminated mirrors was nearly restored to that of uncontaminated mirrors and the scattering level was reduced. An additional discharge, in which the mirror surface faced the electrode, degraded the reflectance but produced no appreciable change in the scattering level.

Optical Properties of CeO2 Crystal in the Photon Energy Range of 2.5–40 eV

Optical reflectance spectra of CeO 2 crystal have been measured in the photon energy range from 2.5 to 40 eV. A Kramers-Kronig analysis of the reflectance data has been performed to obtain the dielectric function and related functions. The observed spectral features can be explained in terms of the charge transfer and interband transitions and the atomic-like excitation of the Ce 5 p core electron. A peak regarded as a candidate for the “4 f 2 ” feature has been observed at an excitation energy of 13 eV.

In situ dc oxygen‐discharge cleaning system for optical elements

In situ dc oxygen‐discharge cleaning arrangements have been developed at the Photon Factory for the removal of carbon contamination from optical surfaces. A high cleaning rate could be achieved by producing an oxygen plasma close to the optical elements with special care taken to avoid any harmful effects from the discharge; contaminant carbon was completely removed within a few hours, at most. This short exposure time and the use of dry oxygen gas resulted in a restoration of the original ultrahigh vacuum without a bakeout. Results with a Seya‐Namioka beamline for gas‐phase experiments showed a flux enhancement amounting to a factor of 50, and results with a grasshopper beamline showed a nearly complete recovery of the light intensity, even at the carbon K edge.

Resuscitation of carbon-contaminated mirrors and gratings by oxygen-discharge cleaning. 2: Efficiency recovery in the 100-1000-eV range.

The dc oxygen-discharge cleaning of optical elements contaminated by synchrotron radiation has been studied for a variety of contamination levels, optical materials, electrode and reflecting-surface configurations, discharge powers, and exposure times. Cleaning with a proper electrode-surface configuration resulted in the removal of contaminant layers within 1 h even for highly contaminated elements. The reflectance of mirrors and the diffraction efficiency of gratings were almost completely restored after cleaning over the 4-40- eV energy range; the enhancement even amounted to 1 order of magnitude in some cases. This cleaning procedure did not cause any increased roughness; rather, it resulted in a reduced scattering level of contaminated elements. The removal of contaminants also led to a restoration of the grating blaze; essentially, this contributed to an improvement in the inside first-order efficiency around the blazed energy. From the results with controlled power and exposure time, it was shown that an optimum exposure is achieved within several minutes after the disappearance of visible contamination.

Intense positron beam at KEK

Abstract A positron beam is a useful probe for investigating the electronic states in solids, especially concerning the surface states. The advantage of utilizing positron beams is in their simpler interactions with matter, owing to the absence of any exchange forces, in contrast to the case of low-energy electrons. However, such studies as low-energy positron diffraction, positron microscopy and positronium (Ps) spectroscopy, which require high intensity slow-positron beams, are very limited due to the poor intensity obtained from a conventional radioactive-isotope-based positron source. In conventional laboratories, the slow-positron intensity is restricted to 10 6 e + /s due to the strength of the available radioactive source. An accelerator based slow-positron source is a good candidate for increasing the slow-positron intensity. One of the results using a high intensity pulsed positron beam is presented as a study of the origins of a Ps emitted from SiO 2 . We also describe the two-dimensional angular correlation of annihilation radiation (2D-ACAR) measurement system with slow-positron beams and a positron microscope.

Polarization analyses of elliptically-polarized vacuum-ultraviolet undulator radiation

Abstract Polarization measurements have been performed using a reflection polarimeter in the 50–80 eV region for elliptically polarized synchrotron radiation from a helical undulator installed on beamline BL-28 at the Photon Factory. The degree of circular polarization (PC) was found to strongly depend on the photon energy, indicating the importance of a correction for PC in applications of the undulator radiation. The measured Stokes parameters were compared with numerical calculations. The results are discussed in relation to the effects on the polarization of the beamline optics and of the mixing of the bending-magnet radiation.

Bakable superconducting magnet for magnetic circular dichroism and magnetic‐imaging photoemission‐spectromicroscopy studies

An ultrahigh‐vacuum compatible 5.8‐T superconducting magnet system has been designed and constructed for use in magnetic circular dichroism (MCD) and magnetic‐imaging photoemission‐spectromicroscopy (MIPESM) studies. The design considerations and technical details of the cryosystem which is used to enable bakeouts, along with the magnet performance, are described. The experimental setups of the established MCD measurements and the planned MIPESM measurements are presented. An example of the obtained MCD spectra is also given.

Elliptical‐polarization measurements in the vacuum ultraviolet and soft x‐ray regions with a reflection polarimeter

A complete polarization analysis has been successfully achieved for synchrotron radiation beams in the vacuum ultraviolet and soft x‐ray regions using a reflection polarimeter. The Stokes parameters, which provide a full description of the polarization state of light, were experimentally determined along with three polarizing quantities of the polarimeter. The present result indicates the possibility of a simultaneous determination of the optical constants of mirror materials through polarization analyses.