Optimized transition-edge x-ray microcalorimeter with 2.4 eV energy resolution at 5.9 keV

We present measurements from a series of transition-edge x-ray microcalorimeters designed for optimal energy resolution. We used the geometry of the sensors to control their heat capacity and employed additional normal metal features and a perpendicular magnetic field to control the sharpness of the superconducting-to-normal transition. These degrees of control allow an optimal selection of sensor saturation energy and noise. Successive design changes improved the measured energy resolution of the sensors from 4.5 eV full width at half maximum at 5.9 keV to 2.4 eV at 5.9 keV. Sensors with this energy resolution are well matched to applications in x-ray astrophysics and terrestrial materials analysis.