The Gemini Near-infrared Integral-Field Spectrograph (NIFS) will perform near-diffraction-limited imaging spectroscopy at near-infrared wavelengths. In doing this, it will be used with the ALTAIR facility adaptive optics system on Gemini North. The functional and performance requirements for NIFS are defined in the NIFS Functional and Performance Requirements Document (FPRD; SDN0003.02). The NIFS optical design must meet all of the science requirements listed in the FPRD, and must not degrade the AO-corrected image delivered by ALTAIR by more than 20%. This document defines the NIFS optical design requirements that will ensure that NIFS achieves its science goals.

4 Optical Design Specification

4.1 Wavelength Range

NIFS will have a wavelength range from 0.95–2.5 mm.

4.2 Spatial Resolution

NIFS will use a 29 element integral-field unit with 0.1² wide slitlets which project to two pixels at the detector in the spectral direction. The scale in the spatial direction will be ~ 0.05²/pixel on the sky.

4.3 Field-of-View

NIFS will have a field-of-view of 3.0²´3.0².

4.4 Spectral Resolving Power

NIFS will have two-pixel spectral resolving powers of R ~ 5400 in five wavelength bands; 0.94-1.16 mm, 1.14-1.35 mm, 1.49-1.80 mm, 1.95-2.36 mm, and 2.08-2.50 mm.

4.5 Image Quality

NIFS will deliver an image quality such that in monochromatic light > 85% of the light in the telescope focal plane is reimaged into < 1 pixel at the detector with fabrication and assembly tolerances producing no more than 5% degradation of delivered image.

4.6 System Throughput

NIFS will have a system throughput including telescope, blocking filters, grating, and detector, but excluding the ALTAIR optical path, of > 15%.

4.7 Internal Instrumental Background

The internal instrumental background generated by NIFS is required to be less than either the natural background from the observed science field or the dark current of the detector, whichever is greater. At wavelengths of 2.2 mm and longer, the instrumental effective emissivity should be < 1%. At wavelengths of 1.9 mm and shorter, the photon background should be less than one half of the detector dark current at its nominal operating temperature.

To meet this requirement:

· The science instrument must be maintained at a temperature below TBD K.

· Light leaks and other excess thermal emission must be less than the detector dark current.

· Scattered light from night sky airglow emission-lines must be less than detector dark current.

4.8 Ghost Images

Ghost images generated in the NIFS optics must be below TBD.

4.9 Geometrical Distortion

NIFS shall deliver a spatial/spectral image on the science detector with maximum distortion from the designed rectangle pattern of less than 1 pixel.