FIBRE: a broadband submillimeter spectrometer using superconducting bolometer arrays

Abstract

The Fabry-Perot Interferometer Bolometer Research Experiment FIBRE, a protoype submillimeter spectrometer for astronomical observations, is based on a helium-cooled scanning Fabry-Perot and superconducting transition edge sensor bolometers (TES). The TES design takes advantage of a recently discovered method of excess noise reduction by depositing lateral normal metal bars on these devices. A SQUID multiplexer is used to read out the individual detector pixels. The spectral resolving power of the instrument is provided by a Fabry-Perot spectrometer. The outgoing light from the Fabry-Perot passes onto a low resolution grating for order sorting. A linear bolometer array consisting of 16 elements detects this dispersed light, capturing 5 orders simultaneously from one position on the sky. With tuning of the Fabry-Perot over one free spectral range, a spectrum covering Δλ/λ =1/7 at a resolution of ~1/1200 can be achieved. This spectral resolution is sufficient to resolve doppler broadened line emission from external galaxies. FIBRE operates in the 350 μm and 450 μm bands. These bands cover line emission from the important PDR tracers neutral carbon [CI] and carbon monoxide CO. The spectrometer is used at the Caltech Submillimeter Observatory for astronomical observations.