Photon Factory Activity Report 2017 #35 (2018)

BL-3C, BL-14B /2016G050

Development and application of variable-magnification x-ray Bragg optics

Keiichi HIRANO, Hiroshi SUGIYAMA and Yumiko TAKAHASHI
Institute of Materials Structure Science, Photon Factory, 1-1 Oho, Tsukuba, 305-0801, Japan
1 Introduction
The X-ray Bragg magnifier based on asymmetricdiffraction at a nearly-perfect crystal is a useful opticalelement for X-ray radiology and microscopy, and has
been used at synchrotron facilities, for example, for X-ray
microtomography (µ-CT), analyzer-based phase-contrast
imaging and inline holography. One of the most striking
features of the X-ray Bragg magnifier is that it can covera wide range of resolution from submicrometer up tosubmillimeter, thus filling the gap between X-ray
microscopy and radiology. Another attractive feature isthat it can be combined with X-ray single-photoncounting detectors such as PILATUS and Medipix,
opening up a new possibility for high-resolution, widedynamic-range, high-sensitivity and fast X-ray imaging.
In the conventional X-ray Bragg magnifiers, however,it was difficult to change the magnification factor. In
order to solve this problem, we developed a variablemagnification X-ray Bragg optics. Thanks to thetunability of the magnification factor, we can locate aregion-of-interest (ROI) in a sample under low
magnification, and then observe the details of the ROI
under an optimized magnification. Our X-ray Bragg
optics consists of two magnifier crystals in a crossed
arrangement as schematically shown in Fig. 1. The first
crystal magnifies the incident beam in the horizontal
direction while the second crystal does so in the verticaldirection. The glancing angle of each crystal, θj, is set atthe Bragg condition. Here, the subscript j is 1 for the firstmagnifier and 2 for the second magnifier. The φˆ -axis isα sin θ + sin α cos θ sin φ( ) cos
cos α sin θ − sin α cos θ sin φM j φj =j

Bj

j

Bj

jj

Bj

j

Bj

j

where αj is the asymmetric angle and θBj is the Braggangle.
2 Experimental and Results
The experiments were carried out at the verticalwiggler beamline BL-14B of the Photon Factory. First,the white beam from the light source was monochromatedat 0.112 nm by an Si(111) double-crystal monochromator.
Then the monochromatic beam transmitted through asample, and was incident to the variable-magnification xray Bragg optics. As magnifiers, we used asymmetricallycut Si(220) crystals ( θ B1 = θ B 2 = 16.96  , 1 =  2 = 14  ) madeof non-doped float-zone silicon crystal. Magnified x-rayimages were observed by a module of the PILATUS
100K-S pixel detector (Dectris Ltd.). The pixel size was
172 µm (H) × 172 µm (V) and the number of pixels was
487 (H) × 195 (V).
First we estimated the spatial resolution of the entire
optical system at several magnification factors using MTFcharts. The results are shown in Fig. 2. It is clearly seenthat the spatial resolution is in inverse proportion to themagnification factor. In this experiment, we could control
the spatial resolution between 28 µm and 280 µm.

jperpendicular to the diffracting lattice planes of the j-th
crystal, and we can scan the azimuth angle, φj, while
keeping the Bragg condition. The magnification factor ofeach magnifier is given byFig. 2 Spatial resolution of the entire opticalsystem estimated at several magnification factors.

Fig. 1 Variable-magnification X-ray Bragg optics.

Next, we observed a leaf as a sample at severalmagnification factors. For example, Fig. 3 shows theobtained images at M 1 = M 2 = 8.5 . The exposure time was0.25 sec. Although the shape of the leaf is hardly
discernible at a lower magnification, the details of thesample can be clearly seen at the higher magnification.

Photon Factory Activity Report 2017 #35 (2018)

Fig. 3 Obtained image of the leaf at M 1 = M 2 = 8.5 . Theview-field is about 3.5 mm (H) × 3.2 mm (V).
In the experiment we could control the magnification
factor from 1.0 up to 10 with reasonable throughput evenat a second-generation synchrotron radiation facility suchas the Photon Factory. In fact, the exposure time was asshort as 0.3 sec at the maximum magnification factor( M 1 = M 2 = 10 ). A much wider range of magnification
factor will be realized at third-generation synchrotron
radiation facilities where submicrometer resolutions havealready been achieved with the conventional fixedmagnification x-ray Bragg optics using PILATUS andMedipix. We expect that the performance of our variablemagnification x-ray Bragg optics will be maximized atlinac-based x-ray sources such as x-ray free-electronlasers (XFELs) and energy recovery linacs (ERLs), which
can produce diffraction-limited x-rays in both thehorizontal and vertical directions. We hope that our novel
x-ray optical system will open up new possibilities forhigh-sensitivity, wide-dynamic-range, fast and variablemagnification x-ray imaging.
* keiichi.hirano@kek.jp