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Optomechanical Layout

 

The optomechanical layout of the NIFS light path:

 

The NIFS spectrograph optics are shown above. The Gemini facility adaptive optics system (Altair) passes a 120" diameter, f/16 field to NIFS and a small pickoff mirror reflects the central 3."0 x 3."0 field into the spectrograph. The remaining field not vignetted by this probe passes to the NIFS OIWFS, which monitors tip-tilt and focus variations. A focal plane mask wheel at the Altair focal plane baffles the image and allows the insertion of occulting disks. The NIFS spectrograph uses a concentric IFU to reformat the input focal plane. The IFU re-images the focal plane at an enlarged scale onto a concave stack of 29 image slicer mirrors. These mirrors fan the IFU channels and form pupil images on an array of concave pupil mirrors. The pupil mirrors re-image the focal plane at a demagnified scale on an array of fields mirrors where the input field is reformatted as a long thin slit. The field mirrors feed the Bouwers collimator of the spectrograph, which consists of a spherical primary mirror and a concentric spherical meniscus that corrects the aberration of the primary. The essential feature of the overall configuration is that all the optical surfaces of the IFU and spectrograph Bouwers collimator are concentric about a fanning axis through the central image slicer mirror, thus off axis aberrations are eliminated. The geometry of the IFU and the anamorphic magnification of the grating result in spatial pixels that are rectangular (0."1 x 0."04) on the sky. The NIFS spectrograph uses a refractive five-element camera with a focal length of 286mm.

The NIFS spectrograph module is shown below mounted on the cold work surface plate with baffling and the spectrograph cover and skirt removed.