Near-Infrared Integral-Field Spectrograph (NIFS):
An Instrument Proposed for Gemini
Peter J. McGregor , Peter Conroy , Gabe Bloxham , Jan van Harmelen, PASA, 16 (3), 273.

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NIFS Overview

NIFS will be used with the Gemini laser guide star adaptive optics (AO) system. The baseline design is shown in Fig. 1. A

3.2'' x 3.2'' ``stair-case'' IFU feeds a near-infrared spectrograph with four fixed-angle gratings mounted in a grating wheel. A single, fixed-format camera forms the spectral image on a

2048 x 2048 Rockwell HAWAII-2 HgCdTe array. Spectral resolving powers of $\sim$ 5400 will be achieved with complete wavelength coverage in each of the J, H, and K photometric bands through 32 fully sampled 0.1'' wide slitlets. The velocity resolution of $\sim$ 55 km s^-1 is sufficient to achieve the targeted science objectives, and will allow software rejection of OH airglow lines.

**Figure 1:** NIFS baseline optical configuration. The dewar window is shown at left. After passing through an Offner relay, the f/16 beam is converted to f/90 and reimaged onto the image slicer. This is followed by the pupil mirror array and the field mirror array of the IFU which feed the spectrograph. The grating is at lower right. The detector is at lower left.
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Light enters at the left of Fig. 1 through the dewar window and comes to focus 300 mm inside the dewar. The

3.2'' x 3.2'' field passes to an Offner relay which reimages the telescope exit pupil on a small secondary mirror which acts as a cold stop to baffle the system. The f/16 beams from the Offner relay pass through a focal ratio converter which forms an f/90 focus on an 11 mm x 11 mm reflective image slicer (see §5.2) and also forms an f/90 pupil further downstream. The image slicer directs each slice of the focal plane to a different element of the f/90 pupil mirror array where the 32 spherical mirrors reimage the f/16 focal plane in the form of a 64 mm long ``staircase'' slit on the field mirror array. The 32 spherical field mirrors are decentered by increasing amounts so that they feed telecentric beams (i.e., parallel cones) into the spectrograph. The spectrograph uses a doublet field lens to direct these beams towards a 30 mm diameter pupil on the grating at lower right in Fig. 1 via a folding mirror and a doublet collimator lens. A folded camera views the diffracted light with a 30 $^\circ$ Ebert angle and focuses spectra from the 32 slitlets onto the detector at lower left in Fig. 1.

Next Section: NIFS Science Drivers
Title/Abstract Page: Near-Infrared Integral-Field Spectrograph (NIFS):
Previous Section: Introduction
Contents Page: Volume 16, Number 3

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NIFS Overview