A high energy resolution gamma-ray TES microcalorimeter with fast response time

We report on the development of the fast response gamma-ray TES microcalorimeter composed of a bulk Sn absorber coupled to a Ti/Au TES. In order to realize a TES microcalorimeter with a large absorber and a fast response time, besides taking saturation and linearity into account, study of the effect of thermal diffusion in the absorber on energy resolution is essential. Therefore, we performed 3 dimensional simulations using SPICE to calculate the effect of thermal diffusion in the absorber on energy resolution. By fabricating a device with the optimized heat capacity of the absorber and the thermal conductance between the absorber and the TES based on the simulation result, we have demonstrated an energy resolution of 38.4 +/- 0.9 eV at 60 keV with a time constant of 0.5 ms.