| we present a progress report on the design and construction of the field - imaging far - infrared line spectrometer ( fifi ls ) for the sofia airborne observatory . the design of the instrument is driven by the goal of maximizing observing efficiency , especially for observations of faint , extragalactic objects . thus , fifi ls utilizes an integral field technique that uses slicer mirrors to optically re - arrange the two - dimensional field into a single slit for a long slit spectrometer . effectively , a 5 @xmath0 5 pixel spatial field of view is imaged to a 25 @xmath0 1 pixel slit and dispersed to a 25 @xmath0 16 pixel , two - dimensional detector array , providing diffraction - limited spatial and spectral multiplexing . in this manner , the instrument employs two parallel , medium resolution ( r @xmath12000 ) grating spectrometers for simultaneous observations in two bands : a short wavelength band ( 42 to 110 @xmath2 m ) and a long wavelength band ( 110 to 210 @xmath2 m ) . overall , for each of the 25 spatial pixels , the instrument can cover a velocity range of @xmath11500 km / s around selected far - infrared lines with an estimated sensitivity of @xmath3 w hz@xmath4 per pixel . this arrangement provides good spectral coverage with high responsivity . * this paper does not include figures due to astro - ph size limitations . please download entire file at http://fifi-ls.mpe-garching.mpg.de/fifils.ps.gz . * |