Goodman Spectrograph Gratings (New)

Updated Apr 2017.

Up to three (3) gratings can be installed in the spectrograph at a time, in a linear stage which allows the rapid interchange of gratings. Installing different gratings is  a day time operation. No grating installations are done during the night.

The grating complement includes 400, 600, 930, 1200, 1800, 2100 and 2400 l/mm transmission VPH gratings.
 
NEW (Apr 2017):  New 600 and 1200 l/mm VPH gratings have been delivered for Goodman.

Users have now a choice of 600-Blue, 600-old (which is red-optimized), and 1200-Blue or 1200-Red gratings. 
If you are observing in the UV-Blue, do prefer the blue-optimized gratings, otherwise request the 600-old or 1200-Red. 
 
NOTE: The existing 600 l/mm grating is now renamed 600-old. It is a red-optimized grating.

Long Wavelength Limit for High Resolution Gratings
Because of limits in the camera rotation stage, it is not possible to use the 1800, 2100 and 2400 l/mm gratings beyond certain wavelength limits.

The table below shows the dispersion and the wavelength coverage for observations in our set spectroscopic modes.  Please note that the 1800, 2100, and 2400 l/mm gratings are operated in Custom mode where the observer selects the central wavelength for their observations.

The VPH gratings operate via Bragg scattering and their efficient operation requires Littrow or near-Littrow operation of the spectrograph. A grating rotation stage sets the incident angle to the desired value, which depends upon the line density of the grating and the central wavelength of interest. A concentric camera rotation stage must then be set to nearly twice this angle to intercept the diffracted beam.  A set of fixed observing modes for each grating are given below, where applicable.  All gratings can be used in the Custom mode.