Development of the X-ray polarimeter using CMOS imager: polarization sensitivity of a $1.5\mu \mathrm{m}$ pixel CMOS sensor

Abstract

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$$\unicode{x2013}$$30\mathrm{keV}$. A successful proof-of-concept experiment was conducted using a fine-pixel CMOS sensor with a $2.5\mu \mathrm{m}$ pixel size. In this study, we conducted beam experiments to assess the modulation factor (MF) of the CMOS sensor with a $1.5\mu \mathrm{m}$ pixel size manufactured by Canon and to determine if there was any improvement in the MF. The measured MF was $8.32\%\pm 0.34\%$ at $10\mathrm{keV}$ and $16.10\%\pm 0.68\%$ at $22\mathrm{keV}$, exceeding those of the $2.5\mu \mathrm{m}$ sensor in the $6$$\unicode{x2013}$$22\mathrm{keV}$ range. We also evaluated the quantum efficiency of the sensor, inferring a detection layer thickness of $2.67\pm 0.48\mu \mathrm{m}$. To develop a more sensitive polarimeter, a sensor with a thicker detection layer, smaller pixel size, and reduced thermal diffusion effect is desirable.

18 pages, 8 figures, 5 tables, accepted for publication in NIM-A