  Massively multiplexed spectroscopic stellar surveys such as MSE present
enormous challenges in the spectrograph design. The combination of high
multiplex, large telescope aperture, high resolution (R~40,000) and natural
seeing implies that multiple spectrographs with large beam sizes, large grating
angles, and fast camera speeds are required, with high cost and risk. An
attractive option to reduce the beam size is to use Bragg-type gratings at much
higher angles than hitherto considered. As well as reducing the spectrograph
size and cost, this also allows the possibility of very high efficiency due to
a close match of s and p-polarization Bragg efficiency peaks. The grating
itself could be a VPH grating, but Surface Relief (SR) gratings offer an
increasingly attractive alternative, with higher maximum line density and
better bandwidth. In either case, the grating needs to be immersed within large
prisms to get the light to and from the grating at the required angles. We
present grating designs and nominal spectrograph designs showing the efficiency
gains and size reductions such gratings might allow for the MSE high resolution
spectrograph.
