Colloquium on 29 August 2013
Spherical Grating Spectrographs


Title: Spherical Grating Spectrographs
Speaker: Darragh O’Donoghue
Date: Thursday, 29 August 2013
Time: 16:00 - 17:00
Venue: SAAO Auditorium


Since the mid 1800s when the “spectroscope” of Bunsen and Kirchhoff solved the resolution problem in spectra of the Sun and laboratory element discovery, the basic form of the optical spectrometer has remained the same: light to be analyzed illuminates a slit, is collimated, incident on a flat grating, and imaged by a camera. Spectrometers using spherical dispersers were suggested in the late 1970s but have thus far been employed on space platforms, both looking down at the Earth and outward at the Cosmos. Ground-based optical/NIR astronomical spectrometers are the most challenging of the traditional instruments, because of the demands of efficient processing of light at low intensity levels and high resolution. In this talk I will review ground-based astronomical spectrometers and describe new forms of spectrometer built around curved Volume Phase Holographic diffraction gratings. I’ll also show how these novel designs can solve problems in the various forms of the instrument, enabling, in particular, massively multiplexed spectroscopy to be realised at minimal cost. These innovations may be useful to South Africa’s growing appetite for spectroscopic follow-up of surveys originating from the new generation of radio telescopes and LSST.

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