Energy calibration of superconducting transition edge sensors for x-ray detection using pulse analysis

Transition edge sensors (TESs) have been developed to be used as high-resolution x-ray detectors. They show excellent energy resolution and can be used in many applications. TESs are a special kind of calorimeters that can determine small temperature changes after x-ray absorption. Such a temperature change causes a strong resistance change (superconducting to normal-conducting phase transition) that can be measured. The energy calibration of a TES based spectrometer is problematic due to the nonlinear behavior of the detector response. In this article, a method is introduced to calibrate the energy scale of TES spectra. This is accomplished by calculating the energy dependence of the response of the detector operated in electrothermal feedback mode. Using this method a calibration accuracy of a few eV for an x-ray energy of 6 keV can be achieved. Examples of energy dispersive x-ray spectroscopy (EDS) measurements demonstrate the high quality of this method for everyday use of TES EDS detectors in material analysis. However, because the method relies only on a few very general assumptions, it should also be useful for other kinds of TES detectors