Superconducting bolometer current modulator

D. Wilms Floet, J. R. Gao, T. M. Klapwijk +1 more

Jerald Ray Hyde

W. Miao, W. Zhang, Kangmin Zhou +5 more

In this paper, the direct detection behaviors of a superconducting hot electron bolometer integrated with a log spiral antenna are investigated by using Fourier Transform Spectrometer (FTS). We find the response of the bolometer to a modulated signal can be detected by a lock-in amplifier not only from the DC bias current, but also from the output noise power at the IF port of the HEB. We attribute the response in output noise power to Johnson noise and thermal fluctuation noise. Both the current response and the output noise power response measured at different bias voltages can be explained by one dimensional distributed hot spot model. In addition, the frequency response of the hot electron bolometer measured from the response in DC bias current is in good agreement with that in IF output noise power.

M. Dobbs, Martin Lueker, K. A. Aird +44 more

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.

G. N. Gol'tsman

Edgar R. Canavan, Thomas R. Stevenson, Peter C. Nagler +1 more

The sensitivity of a bolometer is in principle limited by the phonon noise, which is a function of the conductance between its absorber and the thermal sink. However, practical issues limit the degree to which conductance can be minimized. For example, in a high-radiation environment, extremely low conductance, or, equivalently, long thermal recovery time, can lead to high data loss. To circumvent such limitations, we are developing a technique of modulating the conductance through the use of pixel-scale superconducting heat switches. We have fabricated bolometer-like test devices consisting of isolated regions connected to a thermal ground plane through narrow aluminum strips. Niobium coils are patterned around the aluminum strips. Flowing current through a coil allows the aluminum to be driven into the normal or high thermal conductance state. We have measured the conductance of these devices as a function of temperature and drive coil current.