Analyses on the operating point dependence of the energy resolution with a Ti/Au TES microcalorimeter

Abstract We examined the performance of a single pixel Ti/Au transition-edge sensor (TES) calorimeter for incident X-ray energies of Al-K α , Cr-K α , and Fe-K α , as a function of the TES resistance. We find that the energy resolution does not always degrade with increasing energy. The best energy resolution of 5.7±0.9 eV at 6.4 keV is obtained, which is possibly even better than the baseline width of 6.5±0.2 eV . Assuming that the noise level is determined by the noise spectrum NS( f ; R ∼ R +d R ( E )) considering the resistance change of d R ( E ), instead of NS( f ; R ) at the operating point, these results may be explained by the fact that the noise decreases at the higher TES resistance. The pulse variation appears to have a minimum at a certain resistance of R+ d R(E)≃48 mΩ , and the best energy resolution for each line is obtained at such an operating point, respectively. The pulse variation could be enhanced when the fluctuation of the TES sensitivity α is large at R +d R ( E ).