Fine-pitch CdTe detector for hard X-ray imaging and spectroscopy of the Sun with the FOXSI rocket experiment

TL;DR

This paper reports the development and successful in-flight demonstration of a fine-pitch CdTe detector for high-sensitivity hard X-ray imaging and spectroscopy of the Sun, improving resolution and efficiency over previous silicon-based detectors.

Contribution

The paper introduces a novel fine-pitch CdTe strip detector with enhanced efficiency and resolution for solar X-ray observations, demonstrating its effectiveness in a rocket experiment.

Findings

Achieved ~1 keV energy resolution at 4-15 keV range.

Demonstrated successful solar imaging with the detector in flight.

Improved detector efficiency and spatial resolution over previous silicon detectors.

Abstract

We have developed a fine-pitch hard X-ray (HXR) detector using a cadmium telluride (CdTe) semiconductor for imaging and spectroscopy for the second launch of the Focusing Optics Solar X-ray Imager (FOXSI). FOXSI is a rocket experiment to perform high sensitivity HXR observations from 4-15 keV using the new technique of HXR focusing optics. The focal plane detector requires < 100 um position resolution (to take advantage of the angular resolution of the optics) and about 1 keV energy resolution (FWHM) for spectroscopy down to 4 keV, with moderate cooling (> -30 C). Double-sided silicon strip detectors were used for the first FOXSI flight in 2012 to meet these criteria. To improve the detectors' efficiency (66 at 15 keV for the silicon detectors) and position resolution of 75 um for the second launch, we fabricated double-sided CdTe strip detectors with a position resolution of 60 um and almost 100 % efficiency for the FOXSI energy range. The sensitive area is 7.67 mm x 7.67 mm, corresponding to the field of view of 791'' x 791''. An energy resolution of about 1 keV (FWHM) and low energy threshold of 4 keV were achieved in laboratory calibrations. The second launch of FOXSI was performed on December 11, 2014, and images from the Sun were successfully obtained with the CdTe detector. Therefore we successfully demonstrated the detector concept and the usefulness of this technique for future HXR observations of the Sun.