Impedance measurements for photon number resolving Transition-Edge Sensors

The complex impedance measurement technique is an established method for the characterisation of Transition-Edge Sensors (TES) bolometers and microcalorimeters. In this report this technique is applied at frequencies up to 250 kHz to Ti/Pd and Ti/Au Transition-Edge Sensors, in the optical and near-infrared wavelength range, to obtain a complete frequency response in the complex plane. From these measurements we obtain information about the logarithmic temperature sensitivity , the logarithmic current sensitivity and on the device thermal parameters, heat capacity C, thermal conductance G and the effective response time eff. All these parameters provide a reasonable understanding of the two different detectors and a discussion about the main differences is also reported.