The GNIRS grating turret contains three gratings, all with an effective first order blaze wavelength of 6.6 µm. The diffracted orders then correspond fairly well to the atmospheric windows at 5, 3.5, 2.2, 1.6 and 1.2 µm for orders 1 through 5 respectively; the order- sorting filters (see list of filters) cover the free spectral range of the individual orders, with some allowance for filter roll-off. A filter for order 6 is also supplied; the orders above 5 don't match the atmosphere particularly well and there is some inter-order contamination at short wavelengths as described in detail on the usage pages linked below.

The resolutions provided by the gratings are tabulated below for the short (0.15"/pix) and long (0.05"/pix) cameras. The values given are with the gratings operated at the blaze peak. Tilts to longer wavelength provide somewhat higher resolution, while tilts to shorter wavelengths provide lower resolution. (The resolution in nm is nearly constant for a given order, regardless of tilt). The quoted resolving powers (lambda / delta lambda) are for a two-pixel slit (many wider slits are available, see the list of slits). The usable wavelength coverage for a single order (expressed as a fraction of the wavelength) may be limited by the order-sorting filter for lower-resolutions at short wavelengths and other related factors; see the usage pages for details by clicking on the linked resolving powers

Notes:
(a) This mode potentially provides R=570 but offers no advantage over R=1700 and is not used in practice.
(b) The cross-dispersed prism provides complete 0.9-2.4um spectra at R=1700 across five orders.

The color coding used in the table is as follows:

Last update June 23, 2005; B. Rodgers
In original form: December 22, 2003; Bernadette Rodgers and Sybil Adams