Development of the X-ray polarimeter using CMOS imager: Polarization sensitivity of a 1 . 5 μm pixel CMOS sensor

We are developing an imaging polarimeter by combining a fine -pixel CMOS image sensor with a coded aperture mask as part of the cipher project, aiming to achieve X-ray polarimetry in the energy range of 10- 30 keV. A successful proof -of -concept experiment was conducted using a fine -pixel CMOS sensor with a 2 . 5 mu m pixel size. In this study, we conducted beam experiments to assess the modulation factor (MF) of the CMOS sensor with a 1 . 5 mu m pixel size manufactured by Canon and to determine if there was any improvement in the MF. The measured MF was 8 . 32%+/- 0 . 34% at 10 keV and 16 . 10%+/- 0 . 68% at 22 keV, exceeding those of the 2 . 5 mu m sensor in the 6- 22 keV range. We also evaluated the quantum efficiency of the sensor, inferring a detection layer thickness of 2 . 67 +/- 0 . 48 mu m. To develop a more sensitive polarimeter, a sensor with a thicker detection layer, smaller pixel size, and reduced thermal diffusion effect is desirable.