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Optical Engineering

Optical design of a near-infrared imaging spectropolarimeter for the Advanced Technology Solar Telescope
Author(s): Vincenzo Greco; Fabio Cavallini
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Paper Abstract

In designing the optics of an imaging multi-etalon spectropolarimeter as a post-focus instrument for the Advanced Technology Solar Telescope (ATST), many constraints must be considered. Among these are the large entrance pupil diameter of the telescope (4 m), the demanded large field of view (≥90  arc sec ), high spectral resolving power (≥200,000 ), and limited field-dependent blue-shift of the instrumental profile [≤3 full width at half maximum (FWHM)], which require Fabry-Perot interferometers of large diameter (≥200  mm ), lighted by highly collimated beams. This implies large optical elements and long optical paths. Moreover, to use interference pre-filters with a relatively small diameter (≤70  mm ) and placed between the interferometers to reduce the inter-reflections in axial-mount, a “pupil adapter” must be included with a further increase of the optical path length. Although a multi-etalon spectropolarimeter works in quasi-monochromatic light, the Fraunhofer lines of interest cover a wide range of wavelengths (850 to 1650 nm), which demands a good chromatic aberration control. A low instrumental polarization (≤0.5% ) is also required to allow a high polarimetric precision. Finally, some secondary optical paths are required to perform the initial instrumental setup and to secure the best instrumental performances. A diffraction-limited optical solution for ATST is described that fulfills all the above requirements in a relative small volume.

Paper Details

Date Published: 12 June 2013
PDF: 10 pages
Opt. Eng. 52(6) 063001 doi: 10.1117/1.OE.52.6.063001
Published in: Optical Engineering Volume 52, Issue 6
Show Author Affiliations
Vincenzo Greco, Istituto Nazionale di Ottica (Italy)
Fabio Cavallini, Istituto Nazionale di Ottica (Italy)


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