Progress toward kilopixel arrays: 3.8 eV microcalorimeter resolution in 8-channel SQUID multiplexer

While multiplexed readout of large arrays of submillimeter-wave transition-edge sensors (TESs) has been successfully demonstrated, the development of multiplexed arrays of TES X-ray microcalorimeters is more challenging. Fast X-ray pulses place stringent demands on the multiplexer dynamic range and bandwidth. In this paper, we describe the ongoing development of a time-division multiplexer (TDM) intended specifically for X-ray microcalorimeters. We present data showing 3.74 ± 0.12 eV resolution (FWHM), measured at 6 keV from a sub- 150 μ s sensor in an 8-channel TDM. In addition, we calculate the number of detectors that can be multiplexed as a function of open-loop system bandwidth, amplifier noise, and detector time constant. We find that with achievable improvements, our architecture will allow readout of a square, kilopixel array of high-resolution microcalorimeters with time constants as low as 50 μ s . TDM is thus well-suited to the requirements of many proposed X-ray astronomy missions, including NASAʹs Constellation-X, ESAʹs XEUS, and ISAS/JAXAʹs NeXT.