Photon Factory Activity Report 2005 #23 Part B (2006)
Instrumentation and Technique

12A/2004G214

X-ray Polarimeter with Multi-layer coated CCD
Shunji Kitamoto*a, Takeshi Watanabea, Jun’ichi Kanaia, Keisuke Sudoha, Jun’ichi Satoha, Yosuke
Ohkuboa, Akiko Sekiguchia, Masahiro Tsujimotoa, Kazuharu Sugaa, Takayoshi KohmurabaRikkyo University, 3-34-1, Nishi-Ikebukuro, Toshima-ku, Tokyo, 171-8501, JapanbKohgakuin University, 2665-1, Nakano-cho, Hachioji, Tokyo, 192-0015, Japan
Introduction
We are developing an X-ray polarimeter using atransmission multi layer filter for the future astronomicalusage. The transmission multi layer has the following
advantages. (1) The imaging is easy by using the imaging
detector. (2) If the band path for the polarization
measurement is designed for soft X-rays, the filter istransparent for the hard X-rays. Thus by using the photon
counting detector with moderate energy resolution, we canuse this polarimeter as an imaging spectrometer for thehard X-rays.
The stand-alone filter of the multi layer has been known
1-2
as a good polarimeter . However the stand alonetransmission multilayer filter is very difficult to handle andis not suitable for the future installation onto a satellite. Amulti layer coated photo-diode has been reported but it can3not image . Therefore we are trying to deposit a multi layer
directly onto the surface of a CCD, especially onto a backside CCD. The multi-layer coated CCD can be an imaging
polarimeter.
Multi Layers
Mo/Si multi layers have high reflectivity for 13.5nm Xrays. The reflectivity of 9 layer-pairs (3 nm Mo and 7 nmSi) for 45deg incident angle is calculated. The peakreflectivity is at 13.5 nm with more than 70% for S
polarization, but ~1% for P polarization. This reflection
property works as a polarization selected band pass filter.
The transmission of the same multi layers on a substrate of
100 nm thick SiO2 is also calculated. This SiO2 thickness is
a design value of the anti-reflection coating of our CCD,
but is possible to make thinner. In the 13.5nm band, P
polarization lights have ~20% transmission, but ~6% for S
polarization. This filter is transparent for x-rays withshort wave length less than 1nm. If we detect thetransmitted x-rays with a position sensitive and energy
resolved detector, such as a CCD, we can measure theimage of a selected position angle for 13.5nm band andalso can perform an ordinal spectroscopic-imaging
observation for short wave length x-rays less than 1nm.
The designed multi-layers (Mo/Si 9 layer pairs) aredeposited onto the CCD at JAXA/ISAS, with a DC
magnetron spattering method. The CCD is a back-side
type, S7170-0909, made by HAMAMATSU Photonics.
The pixel size is 24 µmm square and the number of thepixels is 512×512.

Performance Evaluation
The multi-layer-coated CCD was exposed to the polarized
X-ray beam at the BL-12A in Photon Factory. The BL12A is designed for soft X-ray experiments from 30 eV to1000 eV. A grating spectrometer is installed and theenergy resolution is less than 0.1 nm. We used the beamndfrom 70 eV to 120 eV. In order to block the 2 order light,
a Be filter was used for the experiment from 70 eV to 95
eV and a B filter was used from 94 eV to 120 eV. TheCCD was installed on a rotational rod, which can be
manually rotated from the outside of the vacuum chamber.
The beam is aligned to coincide to the rotational rod. We
measured the detected intensity as a function of the photon
energy and of the rotation angle. Figure 1 shows the ratioof the detected intensity to that of the S polarized beam asa function of the rotational angle for several energies.
We confirmed the multi-layer coated CCD works as an3
imaging-polarimeter . However, more precise experimentis needed for quantitative evaluation. Especially theestimation of the amount of the higher order light and thereduction of it are required.
References[1] W. Hu, T. Hirano, M. Yamamoto and M.Watanabe,
1998, JSR, 5, 732-734[2] Y. Hasegawa, Y. Ueji, K. Okitsu, J.M. Ablett, D.P.
Siddons, and Y. Amemiya, 1998, JSR, 5, 738-740[3] S. Kitamoto et al. 2006, Proc. in SPIE 6266

Figure 4. The CCD before the depositing the multilayer. In order to restrict the depositing area, a coveris installed.
*kitamoto@rikkyo.ne.jp

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