Abstract
We describe the development and fabrication of the sub-millimeter APEX (Atacamapathfinder experiment) bolometer camera (SABOCA) and its installation at the APEXradio telescope in Chile. SABOCA has 37 bolometers for a wavelength of about0.35 mm. The bolometers with superconducting transition-edge sensors are readout by superconducting quantum interference devices (SQUIDs). Time-domainmultiplexing was used to compress 40 readout signals into four output channels, whichare further amplified by superconducting quantum interference filters (SQIF).The multiplexer readout circuit is described in detail. One spare SQUID andtwo spare bolometers have been used as reference to evaluate contributions tothe bolometer noise figure. SABOCA’s electrical noise equivalent power is about7 × 10 − 16 W Hz − 1/2, whereas the optical noise equivalent flux density measured at APEX is better than0.35 Jy Hz − 1/2 (1 Jy = 10 − 26 W m − 2 Hz − 1). The measured bolometer noise exceeds the theoretical estimation by factor of two,possibly caused by excess noise in the transition-edge sensor. Nevertheless theachieved instrumental sensitivity meets the specification given by the APEX board.SABOCA was commissioned as the facility instrument in the spring of 2009.
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