Development of 60 μm pitch CdTe double-sided strip detectors for the FOXSI-3 sounding rocket experiment

FOXSI-3 (Focusing Optics X-ray Solar Imager) is an international sounding rocket experiment to observe hard X-rays from the Sun. The previous two flights successfully demonstrated the efficacy of the concept of direct solar imaging in hard X-ray band. For the third launch scheduled in the summer of 2018, we have fabricated a prototype of the CdTe Double-sided Strip Detector. To evaluate the basic performance, laboratory tests were conducted. Energy resolution (FWHM) of 0.8 keV at 13.9 keV and 1.3 keV at 59.5 keV are confirmed. Since the optic angular resolution is finer than the strip pitch of the detector at the focal plane, sub-strip position determination is important to make full use of the high precision of the optic. To test the possibility of sub-strip resolution, we developed a new method of investigating the detector strips with a fine multi-pinhole collimator. The results of the analysis were highly favorable and we confirmed the sub-strip resolution by making sub-strip images of multi-pinholes and flat-irradiation. The spectral uniformity over the detector is also confirmed using the sub-strip image of flat-irradiation.