A study of white pupil configurations for high-resolution échelle spectrographs

D. P. Sablowski; M. Woche; M. Weber; A. Järvinen; K. G. Strassmeier

doi:10.1117/12.2312476

10 July 2018 A study of white pupil configurations for high-resolution échelle spectrographs

D. P. Sablowski, M. Woche, M. Weber, A. Järvinen, K. G. Strassmeier

Proceedings Volume 10706, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation III; 107066F (2018) https://doi.org/10.1117/12.2312476
Event: SPIE Astronomical Telescopes + Instrumentation, 2018, Austin, Texas, United States

Abstract

White pupil arrangements using parabolic off-axis mirrors are commonly used by instrument designers of high-resolution spectrographs. Their advantage is a non-chromatic, spherical free collimation, an intermediate focus providing the possibility for stray light apertures, and the compression of the beam diameter using a second, a transfer, collimator. However, these arrangements suffer from off-axis aberrations in the field. Many configurations create the intermediate focus, after double-passing the primary collimator, in the vicinity of the spectrograph input. This makes it necessary to introduce small angles at the main collimator, further increasing off-axis aberrations. Furthermore, image curvature is high and requires toroidal surfaces to be added near the spectrograph focus in front of the CCD. In high-precision radial velocity measurements, it is of great importance to properly model the spectrographs transfer function in order to derive exact line positions. Therefore, clean and very well defined spots, even when working near the sampling limit, which can simply be represented by gaussians will benefit such measurements. This point is usually considered less by instrument designers. We have studied several possible off-axis mirror arrangements for white pupil spectrographs and discuss our results here. We focus on the image quality generated by the mirrors, on-axis as well as in the field. We come to the conclusion that a fairly uncommon arrangement provides best performance in the sense of image quality and focus accessibility.

Citation Download Citation

D. P. Sablowski, M. Woche, M. Weber, A. Järvinen, and K. G. Strassmeier "A study of white pupil configurations for high-resolution échelle spectrographs", Proc. SPIE 10706, Advances in Optical and Mechanical Technologies for Telescopes and Instrumentation III, 107066F (10 July 2018); https://doi.org/10.1117/12.2312476

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KEYWORDS

Collimators

Spectrographs

Diffraction

Cameras

Image quality

Glasses

Mirrors

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