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GMOS-N and GMOS-S use identical gratings and all gratings are available with each GMOS. However, some gratings are more heavily used than others and therefore spend more time in the instruments; see the grating statistics for recent semesters. Note in particular that the R600 grating has historically had very limited use and is now restricted to Classical programs only. Queue programs wishing to use this grating should consider whether their science requirements can be accommodated with the R400 or R831 grating instead.

A new R150 grating has been available at GMOS-N since December 2016. See details here.  

The table lists the properties of the GMOS gratings based on laboratory measurements. The resolving power R is given at the blaze wavelength, and refers to the resolution achieved with a slit width of 0.5 arcsec. The effective slit width of the IFU in the dispersion direction is 0.31arcsec, see the IFU grating/filter combination page for details.

Efficiency curves based on laboratory data are available. Note that the new GMOS-S Hamamatsu detectors have significant quantum efficiency at 1 µm, falling below 5 percent for wavelengths longer than ~ 1.07 µm (see GMOS-S Hamamatsu array page for more details). The quantum efficiency of the old GMOS-S EEV detectors was below 5 percent for wavelengths longer than 1000 nm. The grating efficiencies assumed by the GMOS-N ITC are extrapolations for wavelengths longer than 1 µm and will be updated once all the gratings have been characterized with the new GMOS-N Hamamatsu detectors. There is no laboratory data available for these gratings longward of 1 µm.

None of the gratings are currently officially offered in 2nd order; however tests have shown that the second order mode for the R600 and R831 gratings may be of interest for some applications. Contact your GMOS instrument scientist for more information.

GMOS Gratings
Grating name Grating number* Ruling density
Grating efficiency

GMOS-N / S e2v

GMOS-N / S e2v
GMOS-S GMOS-N / S Hamamatsu

GMOS-N / S Hamamatsu

B1200 G5301 1200 463 3744 143 0.023 data/plot
G5321 164 / 159 0.026
R831 G5302 831 757 4396 207 0.034 data/plot
G5322 235 / 230 0.038
B600 (G5303 replaced 05/2009)
600 461 1688 276 0.045 data/plot
G5323 317 / 307 0.050
R600** G5304 600 926 3744 286 0.047 data/plot
G5324 328 / 318 0.052
R400 G5305 400 764 1918 416 0.067 data/plot
G5325 472 / 462 0.074
R150 (G5306 replaced 12/2016)
150 717 631 1071 0.174 data/plot
G5326 1219 / 1190 0.193

*The grating name is the concatenation of grating and grating number e.g.R831_G5302 for the Gemini North R831 grating.

**The R600 grating is under-utilized and queue programs may have difficulty with completion due to competition for the three grating slots from the other five gratings. Hence the R600 grating is not available for regular queue programs. Classical programs may still request the R600 grating.

*** The coverage in the Hamamatsu array is broader for GMOS-N due to wider chip gaps.