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Washburn Astronomical Laboratories in the University of Wisconsin-Madison Astronomy Department is developing a near infrared (NIR) integral field spectrograph for the 11-meter Southern African Large Telescope (SALT). This instrument will extend SALT’s capabilities into the NIR, providing medium resolution spectroscopy over the wavelength range of 0.8 to 1.7 microns. Formerly known as RSS-NIR, this spectrograph was originally designed to mount at the prime focus of SALT and share a common collimator and spaceframe structure with the visible wavelength Robert Stobie Spectrograph (RSS-VIS). However, to maximize performance of both the instrument and telescope, its configuration has been changed into a fiber fed instrument located in the spectrometer room below the telescope7. This change necessitated the addition of several new components, including a separate collimator; a fiber integral field unit (IFU); a means to inject light from the telescope into the fibers; and a cooled enclosure to house the spectrograph, collimator, and pseudo-slit end of the fiber cable. The new collimator consists of four refractive elements, one of which is calcium fluoride, and requires a new lens barrel and support structure. The new fiber system incorporates a hexagonally arranged 217-fiber IFU and two mini-bundles containing 15 sky fibers each. The IFU is fabricated out of a two-part clam-shell stainless steel ferrule. The existing SALT fiber instrument feed (FIF) mechanism is adapted to position the IFU and sky bundles on sky, while a slave motion on flexure pivots ensures that the fibers remain telecentric. A 42-m protected fiber cable spans the distance between the telescope prime focus and the pseudo-slit in the spectrometer room. The cable is constructed out of four 25mm outer diameter flexible conduits. Within the conduit, each fiber is individually protected in its own Teflon tube. The route of the fiber cable through the telescope requires careful accommodation of controlled bending. The pseudo-slit comprises a line of mini v-groove blocks attached to the slit plate. The slit, collimator, and spectrograph are housed inside a 40 cold enclosure in the SALT spectrometer room. The cooling system, developed by Norlake Scientific to our specifications, carefully controls against thermal shock and humidity. This paper describes the design, integration, and laboratory verification of the reconfigured spectrograph system, as well as our experiences operating in a -40 ambient pressure environment.
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