Self-induced polarization anisoplanatism

Abstract

This paper suggests that the astronomical science data recorded with low F# telescopes for applications requiring a known point spread function shape and those applications requiring instrument polarization calibration may be compromised unless the effects of vector wave propagation are properly modeled and compensated. Exoplanet coronagraphy requires "matched filter" masks and explicit designs for the real and imaginary parts for the mask transmittance. Three aberration sources dominate image quality in astronomical optical systems: amplitude, phase and polarization. Classical ray-trace aberration analysis used today by optical engineers is inadequate to model image formation in modern low F# high-performance astronomical telescopes. We show here that a complex (real and imaginary) vector wave model is required for high performance, large aperture, very wide-field, low F# systems. Self-induced polarization anisoplanatism (SIPA) reduces system image quality, decreases contrast and limits the ability of image processing techniques to restore images. This paper provides a unique analysis of the image formation process to identify measurements sensitive to SIPA. Both the real part and the imaginary part of the vector complex wave needs to be traced through the entire optical system, including each mirror surface, optical filter, and all masks. Only at the focal plane is the modulus squared taken to obtain an estimate of the measured intensity. This paper also discusses the concept of the polarization conjugate filter, suggested by the author to correct telescope/instrument corrupted phase and amplitude and thus mitigate6, in part the effects of phase and amplitude errors introduced by reflections of incoherent white-light from metal coatings.

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