An On-Instrument Wavefront Sensor (OIWFS) designed, built and tested by the National Research Council of Canada (NRC) for the FLoridA Multi-object Imaging Near-IR Grism Observational Spectrometer (FLAMINGOS) is described. The University of Florida is building the FLAMINGOS-2 IR spectrograph for the Gemini Observatory as a near copy of the original multi-telescope FLAMINGOS instrument. NRC/HIA was subcontracted to build the OIWFS based on the Gemini Multi-Object Spectrograph (GMOS) design. The FLAMINGOS-2 OIWFS patrols the bulk of the FLAMINGOS-2 field-of-view and will accept the Gemini f/16 input beam as well as the f/30 beam from the Gemini Multi-Conjugate Adaptive Optics (MCAO) system. The portion of the probe arm that enters the FLAMINGOS-2 field-of-view is cooled, to avoid contaminating the infrared images. The OIWFS uses the same CCD and CCD controller as was used on GMOS (e2v CCD39 and ARC GENII). Mechanically, the OIWFS is a modified version of the GMOS OIWFS. It comprises two stacked rotational stages, each operating on a single bearing. The top stage supports an optics package, which includes a lenslet array, pickoff arm and CCD. The optical design uses a four subaperture Shack-Hartmann lenslet array. The mechanism is controlled using EPICS based software that includes GUI engineering screens. Test results showing the OIWFS to be fully compliant with design specifications are presented.
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