A frequency-domain read-out technique for large microcalorimeter arrays demonstrated using high-resolution γ-ray sensors

Cryogenic sensors composed of transition-biased superconducting films have demonstrated remarkable sensitivity at gamma-ray, x-ray, optical, and far-infrared to millimeter wavelengths. However, for these sensors to find widespread application in astronomy and materials analysis, technologies for building and reading out large arrays are required. We are currently developing a frequency-domain multiplexing scheme for the read-out of large numbers of microcalorimeters using a much smaller number of amplifiers. In this scheme, each sensor is biased at an identifying frequency and operated in a series LC circuit to suppress out-of-band noise. Here, we present results demonstrating the undegraded operation of two gamma-ray sensors multiplexed using this technique. In addition, we provide a series of design rules which relate the minimum bias frequency and the values of the reactive elements in the system to a small number of sensor properties. Finally, we discuss the ultimate limits on the number of sensors that can be measured with a single amplifier.