| Summary: | The South Pole Imaging Fabry-Perot Interferometer (SPIFI) is the first instrument of its kind -- a direct-detection imaging spectrometer for astronomy in the submillimeter band. SPIFI's focal plane is a square array of 25 silicon bolometers cooled to 60 mK; the spectrometer consists of two cryogenic, scanning Fabry-Perot interferometers in series with a 60 mK bandpass filter. The instrument operates in the short submillimeter windows (350 microns, 450 microns) available from the ground, with spectral resolving power selectable between 500 and 10000. At present, SPIFI's sensitivity is within a factor 1.5-3 of the photon background limit, comparable to the best heterodyne spectrometers. The instrument's large bandwidth and mapping capability provide substantial advantages for specific astrophysical projects, including deep extragalactic observations. In this article we present the motivation for and design of SPIFI and its operational characteristics on the telescope.
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