Sensitivity limits

Even on the excellent site of Chajnantor the sensitivity of any broadband bolometer will be limited by the fluctuations of the ambient thermal background radiation of the telescope and the atmosphere. The best existing bolometer arrays, MAMBO and SCUBA, already operate close to that limit. No doubt this limit can be achieved with different bolometer technologies. For fully efficient pixels, even the conventional semiconducting bolometers can achieve the background limit. The attraction of the superconducting bolometers to be used for LABOCA is in the promise of cryogenic multiplexing and readout via SQUIDs. The superconducting bolometers will also give a faster response time, but not necessarily increased sensitivity. LABOCA will not yet use multiplexing, but will be a necessary first step toward this goal. The size of LABOCA was chosen to represent a significant step in throughput beyond the 117-element MAMBO, while still being feasible with parallel readout.