The NIRI entrance window is made of CaF2 and is 180mm in diameter and 20mm thick with radius of curvature of 4000mm on both surfaces. The outer window surface is at ambient temperature/pressure while the inner surface will reach cryogenic temperatures at vacuum (<10^-5 torr). The window provides a clear aperture of 145mm diameter and has a wedge tolerance specification of <0.5 arcminutes. The outer surface is anti-reflection coated for the 1-5.6um wavelength range.

In the photograph below, the entrance window aperture is shown covered by a plexiglass disk to keep moisture from condensing on the CaF2 window during testing at sea-level. This will be removed when NIRI is in use on Gemini. Through the window can be seen the focal-plane pin-hole mask used in image quality characterisation.

The NIRI beam-splitter wheel contains three beam-splitters to direct the science beam and OIWFS (On-instrument wavefront sensor) beam to the appropriate on-board instruments. The beam-splitters are flat mirrors of different sizes to allow the OIWFS beam for each camera, f/6, f/14 and f/32, to be picked off without modifying the science field. The beam-splitters therefore, send the available field (dependent on the science camera in use) surrounding the science field, to the OIWFS which operates in the near-IR using a Rockwell 1024x1024 near-IR array detector. The photo below shows the beam-splitter wheel in-situ in the NIRI dewar. The wheel holds three beam-splitters (one to the right, one to the left and one at the bottom of the wheel) and an alignment pin-hole mask for the OIWFS

The photo below shows the entrance window at the bottom and the f/32 beam-splitter mirror located over the focal-plane pin-hole mask in the focal-plane mask wheel. To the left of the f/32 mask is a larger beam-splitter, the f/6 unit, and to the right is the third beam-splitter, the f/14 unit. All three beams-splitters are mounted on the beam-splitter wheel.

Below is shown a closer view of the f/32 beam-splitter. The telescope beam enters the photo from the bottom where it is deflected 90 degrees by the beam-splitter (into the photo). Next, the beam passes through the focal-plane mask wheel set, in this photo, to the pin-hole mask position.

The focal-plane mask wheel is located immediately after the science channel/OIWFS (on-instrument wavefront sensor) beamsplitter wheel and is located at the telescope focal-plane within NIRI. This wheel contains the slits and masks required for spectroscopy and polarimetry, respectively. The wheel is shown below prior to the installation of NIRI components further down the science channel. The wheel has a diameter of ~550mm and can hold up to 12 slits/masks.

Two sizes of square apertures are seen in the FP Mask wheel, the larger apertures are for f/6 (R~1000-2000, long-slit [100'], full passband [J, H, K, L, M]) spectroscopy while the smaller apertures are for f/14 (R~2000-4000, long-slit [50'], partial passband [J, H, K, L, M]) spectroscopy. The slits expected to be available in f/6 mode are of width 0.23' and 0.46' (2- and 4-pixels, respectively) and in f/14 mode they are 0.1' and 0.15' (2- and 3-pixels, respectively).

The photo below shows a close-up of the FP mask wheel after installation of the rest of NIRI's optical/mechanical components. Some slits/masks are inserted in the wheel. The mask at the centre of the photo is a pin-hole mask for alignment and image quality tests. The grey rectangle partially obscuring this mask is the beam steerer mirror which splits the field into a science beam and OIWFS beam. In the photo, entrance window of NIRI is at the bottom and the science beam is deflected by 90 degrees through the pin-hold mask into the science instrument. The OIWFS beam, the area of the field around the science field, passes straight through (undeflected) and enters the OIWFS instrument at the top of the photo.

The field lens transfers the telescope beam onto the fold mirrors which in turn pass the beam to the filters wheel and collimator lens. Below will be a photo of the field lens installed in the science instrument (once one has been taken). The field lens is a single component spherical lens made of ZnSe It is 138mm in diameter. The field lens reduces (?) the telescope beam f-ratio to Y.

The two fold mirrors are fused silica lambda/20 rectangular flats (125mmx90mm and 115mmx80mm, respectively) that re-direct the telescope beam from the field lens to the first of two filter wheels. There location is indicated in the photo below. The telescope beam passes vertically upwards from below the optical table, labeled in the photo, to the first fold mirror which bends the beam through 90 degrees to be parallel to the optical table. The second fold mirror bends the beam through 90 degrees parallel to the optical table to filter wheel #1. The fold mirrors are enclosed in aluminum housing (the black box) and are not directly visible in the photo.

The NIRI filter wheels are 530mm in diameter and each contains 12 apertures for mounting near-IR filter. Filter wheel #1 is located immediately after the two fold mirrors and is in the uncollimated telescope beam. This filter wheel will hold broad band near-IR filters i.e. those not as sensitive to the collimated nature of the incident radiation. Filter wheel #2 is located after the collimator lens in the collimated beam and will hold narrow band near-IR filters e.g. interference filters for line and narrow band continuum work. Below is a photo of a filter wheel, in its protective and baffling housing, outside of NIRI. The design of the filter wheels (and the pupil mask/filter wheel) is modular in that the can be easily removed from NIRI.

The filter wheels slide into slots in the science path optical table. These slots can be readily seen in the photo below. Filter wheel #1 has its own slot while filter wheel #2 shares a wider slot with the pupil mask/filter wheel.

The photo below shows the two filter wheels and pupil mask/filter wheel mounted in the NIRI optical path, the collimator can be seen between the two filter wheels.

Below is a photo of a near-IR filter mounted in a filter holder and inserted into the NIRI filter wheel. The filters acquired for NIRI are from the Mauna Kea Filter Consortium set defined by the Gemini Observatory and University of Hawaii. The filters are 50mm in diameter and have optimized bandpass. See the NIRI imaging filters page for more information.

Filter wheel #1 sitting in its opened cassette:

Filter wheel #3 completely removed from its cassette. The five tilted red elements are the f/6 grisms(J,H,K,L,M), and the three clear ones are the f/32 grisms (J,H,K). The open position at the bottom is the pupil mask.

The NIRI collimator lens is a two element lens made of LiF and BaF2. The first lens are both spherical with the first being a meniscus while the second is plano-convex. They both have a diameter of ~55mm. It is located between the two filter wheels on the science path optical table. Below are two photos of the collimator unit without the filters wheels mounted on the table.

Below is a photo of the science path optical table showing the collimator lens, two filter wheels and pupil mask/filter wheel all mounted.

The pupil mask/filter wheel is of a similar design as the two filter wheels, is 530mm in diameter and contains apertures for up to 12 masks and filters. The nominal pupil image has a diameter of 36mm. In fact, this is where the 5 NIRI grisms (transmission grating prisms) are located to facilitate observations in its spectroscopic mode. Also, mounted here is a Wollaston prism analyser (for imaging polarimetry observations) together with a selection of masks/stops (for alignment and background suppression) and a PK50 thermal-IR flux blocker. Coronographic masks will also be placed in the this wheel. The design of the pupil mask/filter wheel, again, modular in that the wheel and housing can be easily removed from NIRI. Below is a photo of the pupil mask/filter wheel prior to installation in NIRI.

The photo below shows a closer view of the two holes in the pupil mask/filter wheel. The larger hole is the mask/filter access hole while the smaller hole is the telescope beam path through the wheel.

The current NIRI grisms have been designed to give a spectral resolution of between 2000 and 4000, are direct-ruled KRS-5 and made by Zeiss in Germany. Each grism costs approximately $16000. KRS-5 has a higher index of refraction than other, more typical, grism materials and hence, for a smaller path length a larger dispersion is obtained. Below is a photo of one of the 5 NIRI grisms in its holder ready for mounting in the pupil mask/filter wheel.

The view below shows a different perspective on the KRS5 grism showing its compact size.

The Wollaston prism analyser for imaging polarimetry with NIRI is shown in the photo below. The prism is made of MgF2 and is ~47mm is diameter and hexagonal in shape. It produces a spatial separation of orthogonal polarization components (the o- and e-rays) of incident radiation of ~3.7" (32 pixels using the f/6 camera) on the NIRI science detector. The Wollaston prism will be used in conjunction with the GPOL polarimetric retarder unit located external to NIRI in the A&G box above the Instrument Support Structure (the ISS). For imaging polarimetry of extended sources a focal plane mask blocking radiation from sections of the array will be used. In these regions the radiation from the orthogonal polarization state will be imaged (after spatial displacement by the analyser).

The pupil viewer optics are used in conjunction with the f/32 camera to produce an image of the pupil (the Gemini secondary, M2) on the near-IR detector. This is very useful for alignment purposes. The pupil viewer optics consist of three spherical lenses of diameter 60mm which are made of ZnSe (2) and BaF2. The photo below shows one of the lenses in it position in NIRI but out of the telescope beam. The f/32 camera barrel has been removed and would normally be positioned between the mount labeled 'optical path' and the beam splitter mirrors to the right (not in the photo).

Below is a photo of the second pupil viewer lens, located below the optical table, in the withdrawn position.

Below is an (unflattened) L-band image of the pupil taken in June 2006. The pupil fills approximately 90% of the array with a spatial resolution of about 3-4mm on the surface of the secondary (M2) mirror.

The f/6 camera optics provides NIRI with a wide-field imaging mode at a pixel scale of 0.116"/pixel and a fov of ~2'. The f/6 camera lens is a multi-component (4) lens of diameter ~80mm made of BaF2, ZnSe, LiF and ZnS. All but two surfaces are spherical with one ZnSe and ZnS surface being aspheric. The top of the wide-field f/6 lens can be seen in the photo below. The collimated telescope beam (from the collimator lens, seen at the edge of the photo, to filter wheel #2 and the pupil mask/filter wheel) enters the photo at the bottom, encounters beam steerer #1 (a flat mirror) and, for the f/6 camera, is deflected downwards, to the f/6 lens and through the optical table.

The f/14 camera optics provides NIRI with an imaging mode optimized for the image quality obtainable with tip/tilt M2 correction at a pixel scale of 0.050"/pixel and a fov of ~50". The f/14 camera lens is a multi-component (4) lens of diameter ~70mm made of BaF2, ZnSe, LiF and ZnS. All surfaces are spherical. The f/14 lens barrel (and the outer lens at the centre of the photo) can be seen in the photo below. The collimated telescope beam (from the collimator lens, seen at the left edge of the photo, to filter wheel #2 and the pupil mask/filter wheel) enters the photo from the left, encounters beam steerer #1 (a flat mirror) and, for the f/14 camera, is deflected to the left, to the f/14 lens. At the end of the f/14 camera lens is a flat mirror that directs the beam downwards and through the optical table.

The f/32 camera optics provides NIRI with a narrow-field imaging mode optimized for the image quality obtainable with adaptive optics (AO) correction at a pixel scale of 0.022"/pixel and a fov of ~22". The f/32 camera lens is a multi-component (4) lens of diameter ~60mm made of BaF2, ZnSe, LiF and ZnS. All surfaces are spherical. The f/32 lens barrel can be seen in the photo below. The collimated telescope beam (from the collimator lens, seen at the left edge of the photo, to filter wheel #2 and the pupil mask/filter wheel) enters the photo from the left, encounters beam steerer #1 (a flat mirror) and, for the f/32 camera, is deflected to the right, to the f/32 lens. At the end of the f/32 camera lens is a flat mirror that directs the beam downwards and through the optical table.