Single-exposure wide-wavelength-coverage echelle spectrograph

We present the design for an echelle spectrograph for 6.5 m telescopes: i.e. the converted MMT and Magellan. We incorporate fused silica prism cross dispersion for higher transmission, and use a single camera that records simultaneously full 300 - 1100 nm wavelength range of CCD detectors. The broad wavelength coverage in a single exposure will make this a powerful instrument for many scientific problems: i.e. the study of the metallicity, evolution and clustering of the primordial Lyman alpha forest, tracing the nucleosynthetic history and element depletion pattern in the ISM of high redshift galaxies, determining if dark-matter halos are ubiquitous, and studying metal abundance analyses of stars. Six detectors are placed tangent to the focal sphere of a Schmidt camera. Each has its own thin field flattener. In this way excellent image quality is maintained while the obscuration by the detector array is minimal, even though it is big enough to cover the entire cross dispersed spectrum. Each back-illuminated CCD is dedicated to a limited spectral range, and can be given appropriately optimized coatings for highest efficiency. Designs for 20 and 30 cm beams have been produced, both using 60 cm Schmidt plates and achieve resolving power slit width products of 50,000 arc seconds. The 2048 square CCDs yield spectral resolution sampling of 200,000/pixel. The `point and shoot' character of the spectrograph should result in simplified controls and software.