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 the R600 grating in particular is rarely installed in either GMOS; queue programs should carefully consider whether their science requirements could be accommodated with either the R400 or R831 gratings instead.

There is a new B600 grating is available at GMOS-N since May 2009. 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 quantum efficiency of the GMOS-S EEV detectors is below 5 percent for wavelengths longer than 1000 nm. The new GMOS-N Hamamatsu detectors will have significant quantum efficiency at 1 µm, falling below 5 percent for wavelengths longer than ~ 1.07 µm. There is no laboratory data available for these gratings longward of 1 µm. 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.

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.

*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. Classical programs can request the R600 grating with no difficulty.