D. Schwan

Frequency multiplexed superconducting quantum interference device readout of large bolometer arrays for cosmic microwave background measurements

A technological milestone for experiments employing transition edge sensor bolometers operating at sub-Kelvin temperature is the deployment of detector arrays with 100s-1000s of bolometers. One key technology for such arrays is readout multiplexing: the ability to read out many sensors simultaneously on the same set of wires. This paper describes a frequency-domain multiplexed readout system which has been developed for and deployed on the APEX-SZ and South Pole Telescope millimeter wavelength receivers. In this system, the detector array is divided into modules of seven detectors, and each bolometer within the module is biased with a unique ∼MHz sinusoidal carrier such that the individual bolometer signals are well separated in frequency space. The currents from all bolometers in a module are summed together and pre-amplified with superconducting quantum interference devices operating at 4 K. Room temperature electronics demodulate the carriers to recover the bolometer signals, which are digitized separately and stored to disk. This readout system contributes little noise relative to the detectors themselves, is remarkably insensitive to unwanted microphonic excitations, and provides a technology pathway to multiplexing larger numbers of sensors.

Further Optimization of the APEX‐SZ TES Bolometer Array

We describe the recent reoptimization of the detector array in the APEX‐SZ receiver, which is currently operating at the APEX telescope in Chile. APEX‐SZ is designed to image the Sunyaev Zel’dovich effect (SZE). Observations are made in a single spectral band centered on 150 GHz, which is where the decrement of the SZE peaks. The APEX‐SZ transition‐edge sensor bolometers are micro‐fabricated in six 55‐element sub arrays, which combine to form the full 330‐element focal plane operating at 280 mK. We report on the newest generation of sub‐arrays that use a λ/4 silicon‐filled backshort. Compared to the first generation array which used a 3λ/4 backshort, the new arrays have a broader bandwidth and an increased optical efficiency. We present spectral bandpass and efficiency measurements and compare these to electromagnetic simulations of the bolometer absorption. The overall improvement in optical coupling reduces the noise equivalent temperature (NET) of each bolometer by a factor of approximately 1.5. Severa...

New technologies for the detection of millimeter and submillimeter waves

Voltage-biased superconducting bolometers have many operational advantages over conventional bolometer technology including sensitivity, linearity, speed, and immunity from environmental disturbance. A review is given of the Berkeley program for developing this new technology. Developments include fully lithographed individual bolometers in the spiderweb configuration, arrays of 1024 close-packed absorber-coupled bolometers, antenna-coupled bolometers, and a frequency-domain SQUID readout multiplexer.