Yoshiyuki Tsusaka

Characterization of the Advanced Satellite for Cosmology and Astrophysics x-ray telescope: preflight calibration and ray tracing

The x-ray properties of multinested thin-foil mirror x-ray telescopes (XRTs) on board ASCA, the Advanced Satellite for Cosmology and Astrophysics, were fully evaluated with an x-ray pencil beam.Scanning over the telescope aperture of 35 cm in diameter with an x-ray pencil beam, we found the effective area of a set of XRTs to be 325, 200, and 113 cm(2) at energies of 1.5, 4.5, and 8.0 keV, respectively. We derive the point-spread functions (PSFs) of the XRTs by measuring the image profile at the focal plane with an x-ray CCD. The PSF is found to exhibit a sharp core concentrated within 30 arcsec and a broad wing extended to 3 arcmin in half-power diameter. We also evaluate the contribution of stray light, which is caused by the single reflection of x rays by primary or secondary mirrors and by the backside reflection of the mirrors. To obtain the characteristics of the XRT in the energy region of 0.5-10.0 keV, incorporated with the measurements at discrete energies, we develop a ray-tracing method with the telescope design parameter, the PSF, and optical constants. In particular, we obtain the optical constants around the gold-atom M shell (Au-M) absorption-edge energies by measuring the reflectivity of our mirror sample, with monochromatized x-rays in the energy range of 2.0-3.5 keV from synchrotron radiation. Taking into account the PSFs and optical constants, we find that our ray-tracing program can reproduce all these XRT performances.

Hyogo beamline at SPring-8: multiple station beamline with the TROIKA concept

Abstract The Hyogo beamline has been constructed as the first contract beamline at SPring-8. It has three experimental hutches and their corresponding three monochromators. Two upstream transparent monochromators enable us to perform three experiments for different purposes simultaneously. Employing a figure-8 undulator, horizontally or vertically polarized X-rays can be obtained in a wide energy range. Rocking curves of the monochromators were almost identical to theoretical ones.

PHASE-CONTRAST X-RAY IMAGING USING BOTH VERTICALLY AND HORIZONTALLY EXPANDED SYNCHROTRON RADIATION X-RAYS WITH ASYMMETRIC BRAGG REFLECTION

Results of phase-contrast X-ray imaging are presented. The optical system employed consisted of a successive arrangement of horizontal and vertical (+, -) double crystals taking asymmetric Bragg reflection with an asymmetry factor of ~0.2. The original beam size was thus expanded in both directions and the field of view actually obtained was ~5×5 mm2. Boundary structures in samples were clearly observed with much higher contrast than those obtained in conventional absorption-contrast imaging. Since this method works in real time, it will provide a new X-ray imaging diagnosis technique for in situ observation over a large area of the samples.

10 keV X-Ray Phase-Contrast Microscopy for Observing Transparent Specimens

Hard X-ray phase-contrast microscopy has been performed with phase plates of tantalum using an X-ray beam from an undulator in SPring-8. The photon energy was set at 10 keV near the L3 absorption edge of tantalum (9.9 keV) in order to increase the phase contrast. To demonstrate its capability, a transparent specimen was imaged clearly in the reverse contrast with phase plates to shift the phase by one-quarter and three-quarters of a period, while conventional absorption imaging showed little contrast. Further, an image contrast as high as approximately 40% can be obtained for the cell walls of another specimen.

X-ray phase-contrast imaging with submicron resolution by using extremely asymmetric Bragg diffractions

We have obtained x-ray phase-contrast images with high spatial resolution by using extremely asymmetric Si 111 Bragg diffractions near the critical angle of the total reflection. The x-rayimage could be magnified to 294 times in both vertical and horizontal directions. By using this x-ray microscopy system, we have observed clear phase-contrast images of a 0.7-μm-wide gold-line pattern.

Sub-15 nm Hard X-Ray Focusing with a New Total-Reflection Zone Plate

A new total-reflection zone plate that consists of a reflective zone pattern with varied-space on a flat substrate was fabricated for hard X-ray nanofocusing. This device is much easier to fabricate than other focusing devices. This is because its focusing size is much smaller than its finest constituent structure since it exploits the effect of glancing X-rays by having a small total reflection angle. Its focusing properties were evaluated using 10-keV X-rays and a focusing size of 14.4 nm was achieved.

Scanning Differential-Phase-Contrast Hard X-Ray Microscopy with Wedge Absorber Detector

A new and simple idea for scanning differential-phase-contrast (S-DPC) hard X-ray microscopy has been proposed. It only uses a wedge absorber coupled with two intensity detectors, and is much more sensitive to sample structures than absorption contrast. It can also extract pure quantitative one-dimensional phase gradient given by a sample without an effect of sample absorption. The S-DPC microscope has been constructed at BL24XU of SPring-8, and its feasibility has been successfully demonstrated at the photon energy of 10 keV by clearly visualizing structures of samples. Further, the experimental phase gradient profile agrees well with simulation. By integrating the resultant phase gradient, the corresponding phase shift distribution could be also imaged.

Formation of Parallel X-Ray Microbeam and Its Application

We have developed a parallel X-ray microbeam of 7×5 µm2 in size with a small angular divergence, which aims high-resolution strain measurements in a very local area. The microbeam has been formed by compressing and collimating the X-rays from a third-generation undulator source using successive asymmetric reflections. Using this beam, we have evaluated the strain induced by field oxidation in silicon wafers by rocking curve measurements. We have observed that the lattice constant in the Si region near the oxide film edge is contracted and that in the SiO2/Si region is extended. The difference between these lattice constants is as small as about Δd/d~±5×10-6.

High-resolution microbeam x-ray diffractometry applied to InGaAsP/InP layers grown by narrow-stripe selective metal-organic vapor phase epitaxy

We measure the diffraction peaks of InGaAsP selective metal-organic vapor-phase epitaxial layers on 1.7-μm-wide InP stripe regions between a pair of SiO2 mask stripes. This is achieved by using an x-ray microbeam with low angular divergence and a narrow energy bandwidth that was produced through two-dimensional condensation of undulator radiation x rays from a synchrotron light source using successive asymmetric diffraction. The lattice strain is investigated by changing the SiO2 mask width from 4 to 40 μm. The rocking curves reveal clear peak shifts in the InGaAsP layers from the higher angle side to the lower angle side of the InP substrate peaks as the mask width increases.

High-Spatial-Resolution Phase Measurement by Micro-Interferometry Using a Hard X-Ray Imaging Microscope

With the aim towards high-spatial-resolution phase measurement, a novel hard X-ray micro-interferometer using an imaging microscope has been proposed and constructed at Hyogo-BL of SPring-8. It is a wavefront-division-type interferometer consisting of a twin zone plate arranged in the same plane. We have succeeded in producing good interference fringes with a visibility of as high as 60% at the photon energy of 9 keV. The fringe scanning method was applied to retrieve phase-shift distribution of a sample. The phase-shift distribution of a 75-µm-thick kapton film and polystyrene microparticles could be imaged clearly with a spatial resolution of 160 nm and the obtained phase shift agreed well with the expected value.