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We are developing a Bragg crystal polarimeter which has high modulation factor. The point we aim is to bend the
crystal; by using bent crystal, we can reflect X-ray emission with broadened energy width, focus it on a small detector,
which increases S/N ratio, and obtain imaging capability. We bent Si (100) crystal sheets by depositing Diamond-Like
Carbon (DLC) on the backside of reflection surface. They are bent by the residual stress between the DLC and crystal.
We can control the curvature by changing the DLC thickness. The angular reflectivity was measured with the line
emission at 8.04 keV (Cu-Kα). We confirmed that the angular width is broadened to 1 degree, which is equivalent to the
energy width of 0.5 keV. The integrated reflectivity becomes larger, as the curvature radius of crystal becomes small.
The modulation factor of bent Si is 0.74, which is higher than that of the flat Si of 0.51. Having the wide energy band
with the high modulation factor, the bent Si crystal can be a new tool for the X-ray polarimeter. We have also made the
bent Ge(111) crystal and measured the same performances. The modulation factor of both the flat and the bent Ge were
0.99 , when using the 8.04 keV (Cu-Kα) beam, as we expected. This means that by choosing crystals, we can make
efficient observations with aimed energy band. We report the status of our development.
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