| Transition-edge sensor (TES) calorimeters are an attractive technology for precision measurements of electromagnetic radiation. However, in order to have a high-energy resolution detector, a small detector volume must be used, thereby limiting the count-rate and efficiency of the detector. As a result, many TES calorimeters must be operated simultaneously in order to achieve an appreciable detector count rate and stopping power for gamma-rays. In order to avoid the thermal load, mechanical complexity, and electrical complexity associated with having dedicated wiring and an amplifier for each sensor, it is highly desirable to develop techniques to read out multiple sensors with a single amplifier.; In this thesis, we investigate the use of frequency-domain multiplexing to read out an array of TES calorimeters. We present a frequency-domain multiplexing measurement in which two gamma-ray calorimeters are measured with a single amplifier and demonstrate that the energy resolution of the sensors is unaffected by multiplexing and that cross-talk between the sensors is negligible. In addition, we discuss the optimal selection of circuit parameters and the limits on the number of sensors that can be measured in this manner. Our results indicate the feasibility of multiplexing 30 sensors or more to one readout line. We also show improvements over previously published work on the energy resolution of our TES calorimeters for x-ray and gamma-ray spectroscopy. Finally, we discuss the behavior of the system under AC bias with respect to the temperature stability of the TES, and we discuss a modification to the general feedback theory necessary due to the operating characteristics of TES calorimeters. |
