Modeling phase variations introduced by extreme broadband dichroics for astronomical photometry

Thurairethinam, Vinooja, Bocchieri, Andrea, Savini, Giorgio, Mugnai, Lorenzo V. ORCID: https://orcid.org/0000-0002-9007-9802 and Pascale, Enzo 2025. Modeling phase variations introduced by extreme broadband dichroics for astronomical photometry. Journal of Astronomical Telescopes, Instruments, and Systems 11 (1) , 014003. 10.1117/1.jatis.11.1.014003

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Abstract

The primary requirement of a manufactured optical surface is a combination of an optimized spectral performance to minimize spectral losses and an accurate mathematical definition of its surface form. Variations in the thicknesses of the coating layers of a dichroic beamsplitter can introduce deviations in the observed phase of the reflected and transmitted beams. Here, we use transmission line modeling to explore the effect of high- and low-spatial frequency variations in the thicknesses of the layers to assess the subsequent impact on the resulting phase of the outgoing beams of a dichroic. We apply our methodology to an extreme broadband dichroic designed to comply with the spectral requirements of a dichroic on the ARIEL telescope. We obtain estimates of the expected phase variations when subjected to high- and low-spatial frequency errors in thickness. We show that these non-uniformities introduce a wavelength-dependent shift in the observed phases of the outgoing beam, which may subsequently degrade the point spread function (PSF) using physical optics simulator (PAOS), an open-source, generic Physical Optics Propagation code, to assess the consequent impact on the PSF at the focal plane of the Fine Guidance System 2 (FGS2) photometer.

Item Type:	Article
Date Type:	Publication
Status:	Published
Schools:	Schools > Physics and Astronomy
Publisher:	Society of Photo-optical Instrumentation Engineers
ISSN:	2329-4124
Date of Acceptance:	27 February 2025
Last Modified:	01 Apr 2025 11:15
URI:	https://orca.cardiff.ac.uk/id/eprint/177307

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