A high-efficiency low-resolution spectrograph design for SALT

We present a concept low-resolution spectrograph design for the Southern African Large Telescope (SALT) based on the O’Donoghue-Clemens Spherical Transmission Grating Spectrometer (STGS) principle. The design delivers R ~ 700 between 380 nm and 760 nm with a peak total efficiency estimated at 45%. This instrument type remains largely invariant with telescope size and can fit into a very compact volume (650 mm × 650 mm × 400 mm). This can truly be a new technology which may transform future instrument design — especially when matched to extremely large telescopes.