X-ray polarimeter with a multilayer-coated CCD

We report a new type X-ray imaging polarimeter: a multilayer-coated CCD. When the X-rays are detected by the CCD, with the incident angle of 45 deg, through the coated multi-layer, the transmissions of the P and S polarized photons are different from each other and we can get an image with a selected position angle of the polarization. By the simulation of the transmission of the multi-layer, we designed an optimal number of the layer-pair and their thickness. The target wave length is 135a, because the Mo/Si multi-layer has a good performance in this energy range. If the dead layer of the back-side CCD is 1000a, nine layer-pairs make the largest difference between the P and S transmission. We deposited the Mo/Si multi-layer directly on a back-side CCD. The CCD was exposed to the polarized photons from synchrotron radiation with 45 deg incident angle. The detected intensity is measured as a function of the photon energy and of the rotation angle around the photon beam. The detection of the polarization is confirmed. However the measured performance is lower than expected. Some possibilities of the cause are discussed.