Volume-phase holographic spectrograph for the Magellan telescopes

We present the design for an optical spectrograph for the 6.5-meter Magellan II Telescope. The spectrograph covers the full visible spectrum in a single exposure at very high efficiency through a dual-channel design and the use of volume phase holographic (VPH) gratings in lieu of traditional surface gratings. A pair of symmetric fold mirrors about the grating keep the spectrograph in Littrow configuration, eliminating the need for an articulated camera. Efficient VPH prescriptions have been developed for all resolution modes up to R=11,000. The resulting design is, mechanically and optically, relatively simple, compact, and inexpensive.