Conservation of étendue in a primary objective grating telescope

Thomas D. Ditto

doi:10.1117/12.2055510

18 July 2014 Conservation of étendue in a primary objective grating telescope

Thomas D. Ditto

Proceedings Volume 9151, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation; 91515T (2014) https://doi.org/10.1117/12.2055510
Event: SPIE Astronomical Telescopes + Instrumentation, 2014, Montréal, Quebec, Canada

Abstract

A novel telescope design that uses a primary objective grating has been shown to have valuable performance features for multiple object spectroscopy as well as a flat collector with relaxed figure tolerances suitable for membrane substrates. The commonly applied figure of merit called étendue takes on new meaning here when compared to telescopes which employ a parabolic mirror In this new telescope design, a mirror is in the secondary. One dimension of the mirror conforms to the familiar metrics for measuring field-of-view and surface area. However, in the other, an anamorphic magnification feature of plane gratings takes effect at angles of diffraction as subtended at grazing off the grating plane normal. When the secondary parabolic mirror is placed at a grazing angle, compression increases exponentially, permitting unprecedented fields-of-view, collection surface areas and aperture in one of the two dimensions. We provide an analysis that calculates the compression, resolution, and field-of-view. More importantly, we study how these parameters are conserved by a secondary parabolic mirror notwithstanding that the mirror diameter can be significantly less than the length of the primary objective grating. Zemax models are used to show that along the dimension of the grating, étendue is conserved in this telescope architecture.

Citation Download Citation

Thomas D. Ditto "Conservation of étendue in a primary objective grating telescope", Proc. SPIE 9151, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation, 91515T (18 July 2014); https://doi.org/10.1117/12.2055510

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KEYWORDS

Mirrors

Telescopes

Diffraction gratings

Diffraction

Spectral resolution

Large Synoptic Survey Telescope

Grazing incidence

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