Y. Ueji

X-ray double phase retarders to compensate for off-axis aberration

An X-ray double phase retarder system composed of two transmission-type phase retarders is proposed and developed in order to compensate for off-axis aberration (phase-shift inhomogeneity due to angular divergence of incident X-rays). The scattering planes of the two phase retarders are set to be inclined by 45 degrees with respect to the plane of incident polarization, but the two phase retarders give Bragg reflections in opposite directions. By using this X-ray optical system, vertically polarized X-rays with a 0.99 degree of linear polarization were obtained from horizontally polarized synchrotron radiation with a horizontal beam divergence of 20 arcsec (0.1 mrad). This value is favorably compared with the value of 0.87 which was obtained using a conventional single phase retarder of identical total thickness, 627 microns. The comparison was made at the nickel K-absorption edge (8333 eV) with the condition that 47% of incident X-rays were transmitted through the two phase retarder crystals. The crystals were (100)-oriented diamond plates giving asymmetric 111 Laue reflections.

Atomic-Scale Structural Evolution upon Crystallite Nucleation and Growth in Amorphous Fe78B13Si9

The structural evolution upon nucleation and growth of nanocrystals was investigated for Fe78B13Si9 alloy. Upon the onset of α-Fe nanocrystallization, free volumes dominantly surrounded by Fe atoms are developed in the intergranular amorphous phase. Along with the growth of Fe-based nanocrystallites, free volumes in the intergranular amorphous phase enlarge and Fe atoms in the surroundings of the free volumes get partially replaced by B and Si. The results suggest that nanocrystallization is associated with a local structural relaxation in the metastable intergranular amorphous phase.

X-ray magnetic circular dichroism imaging with hard X-rays

X-ray polarization-contrast images resulting from X-ray magnetic circular dichroism (XMCD) in the hard X-ray region have been successfully recorded for the first time. The apparatus used consisted of an X-ray polarizer, double X-ray phase retarders, and a high-spatial-resolution X-ray charge-coupled-device detector. The sample used was a hexagonal-close-packed cobalt polycrystal foil having a thickness of about 4 microns. The X-ray polarization-contrast image resulting from XMCD was observed at a photon energy of 10 eV above the cobalt K-absorption edge (7709 eV). The observed contrast in the image was reversed by inversion of the magnetic field. Furthermore, the contrast was reversed again at a photon energy of 32 eV above the cobalt K-absorption edge.

Demonstration of X-ray linear dichroism imaging with hard X-rays.

X-ray polarization-contrast images resulting from X-ray linear dichroism (XLD) in the hard X-ray region have been successfully recorded for the first time. The apparatus used consisted of an X-ray polarizer, double X-ray phase retarders and a high-spatial-resolution X-ray charge-coupled device (CCD) detector. The sample used was a hexagonal close packed (h.c.p.) cobalt single-crystal foil of thickness about 12 microm. The experiment was performed at X-ray energies of 23 and 29 eV above the cobalt K edge (7709 eV), at which the maximum linear dichroisms (approximately 3%) were observed, with their signs reversed, in the XLD spectrum measured with quadruple X-ray phase retarders. The contrasts in the images at the two X-ray energies were reversed as a result of the XLD in the sample. Furthermore, the values of the contrast in the images arising from the linear dichroism (approximately 3%) were in good agreement with those yielded by the XLD spectrum.

Development and application of aberration-compensating x-ray phase retarder systems

X-ray phase-retarder systems to compensate for aberrations which arise from angular divergence and energy spread of x rays, have been developed. The two-quadrant x-ray phase-retarder system consists of two diamond crystals of almost identical thickness. It can compensate for off-axis aberration (phase-shift inhomogeneity due to angular divergence of incident x rays). The four-quadrant x-ray phase-retarder system consists of four diamond crystals of almost identical thickness. The scattering planes of four phase retarders were set to be inclined by 45 deg, 135 deg (= 45 deg + 90 deg), 225 deg (= 45 deg + 180 deg) and 315 deg (= 45 deg + 270 deg), respectively, with respect to the direction of incident polarization. It can compensate for not only the off-axis aberration but also chromatic aberration (phase-shift inhomogeneity due to energy spread of incident x rays). The principles and applications of the two-quadrant and four-quadrant phase-retarder systems will be described.