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The Space Telescope Imaging Spectrograph (STIS) is a second generation instrument to be installed in the Hubble Space Telescope in 1997. It will replace two current instruments: the Faint Object Spectrograph (FOS) and the Goddard High Resolution Spectrograph (GHRS) and incorporate and extend the capabilities of both. As such, the STIS wavelength range extends from 115 - 1000 nm with resolutions from 26 - 100,000. To provide this wide range of capabilities, a complement of 16 diffraction gratings are required for the twelve science modes. The eight low-to- medium resolution modes incorporate first order gratings and four high resolution modes use echelle gratings with first order cross dispersers.
There is a great diversity in grating parameters for the entire complement: groove densities of 24 to 3600 grooves/mm, blaze angles of 0.6 to 70 degrees, operational grating orders from 1 to over 400, as well as the broad spectral range. To acquire gratings of the highest quality for all modes, a program of evaluation and flight selection was initiated. Over 60 breadboard gratings have been obtained from five vendors with nearly all being new rulings to the STIS specifications. Selection and evaluation of the 16 flight replicas is nearly complete. Measurements of surface figure, efficiency, scattering and polarization (for selected gratings) have been made and the results are summarized here.
