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Control of flexure in large astronomical spectrographs

D'Arrigo, Paolo; (1996) Control of flexure in large astronomical spectrographs. Doctoral thesis (Ph.D), UCL (University College London). Green open access

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This thesis describes the design, construction and testing of an experimental system for improving the imaging stability on the detectors of the Intermediate-dispersion Spectroscopic and Imaging System (ISIS), a Cassegrain spectrograph at the 4.2 metre William Hershel Telescope. This system, called ISAAC (ISIS Spectrograph Automatic Active Collimator) is based on the new concept of active compensation, where spectrum shifts, due to the spectrograph flexing under the effect of gravity, are compensated by the movement of an active optical element. ISAAC is a fine steering tip-tilt collimator mirror. The thesis provides an extensive introduction on astronomical spectrographs, active optics and actuator systems. The new concept of active compensation of flexure is also described. The problem of spectrograph flexure is analyzed, focusing in particular on the case of ISIS and on how an active compensation system can help to solve it. The development of ISAAC is explained, from the component specification and design, to the construction and laboratory testing. The performance and successful testing of the instrument at the William Herschel Telescope is then described in detail. The implications for the future of ISIS and of new spectrograph designs are then discussed, with particular stress on the new High Resolution Optical Spectrograph (HROS) for the 8-metre Gemini telescopes.

Type: Thesis (Doctoral)
Qualification: Ph.D
Title: Control of flexure in large astronomical spectrographs
Open access status: An open access version is available from UCL Discovery
Language: English
Additional information: Thesis digitised by ProQuest.
Keywords: Pure sciences; Imaging stability
URI: https://discovery.ucl.ac.uk/id/eprint/10098021
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