II Apodisation

Jacquinot, P.; Roizen-Dossier, B.

doi:10.1016/s0079-6638(08)70570-5

Cited by 175 publications

(129 citation statements)

References 32 publications

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“…We have given a first test of this problem using stepped profiles for the occulter. The sensitivity to error is high but not as strong as in the case of a pupil apodization, which is used to reduce diffraction wing in the sense of Jacquinot & Roizen-Dossier (1964).…”

Section: Discussionmentioning

confidence: 99%

Theoretical performance of solar coronagraphs using sharp-edged or apodized circular external occulters

Aime

2013

A&A

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Context. This study focuses on an instrument able to monitor the corona close to the solar limb. Aims. We study the performance of externally occulted solar coronagraphs. We compute the shape of the umbra and penumbra produced by the occulter at the entrance aperture of the telescope and compare levels of rejection obtained for a circular occulter with a sharp or smooth transmission at the edge. Methods. We show that the umbral pattern in an externally occulted coronagraph can be written as a convolution product between the occulter diffraction pattern and an image of the Sun. We then focus on the analysis to circular symmetric occulters. We first derive an analytical expression using two Lommel series for the Fresnel diffraction pattern produced by a sharp-edged circular occulter. Two different expressions are used for inside and outside the occulter's geometric shadow. We verify that a numerical approach that directly solves the Huygens-Fresnel integral gives the same result. This suggests that the numerical computation can be used for a circular occulter with any variable transmission. Results. With the objective of observing the solar corona a few minutes from limb, a sharp-edged circular occulter of a few meters cannot produce an umbra darker than 10 −4 of the direct sunlight. The same occulter, having an apodization zone of a few percent of the diameter (3 cm for a 1.5 m occulter), darkers the umbra down to 10 −8 of the direct sunlight for linear transmission and to 10 −12 for Sonine or cosine bell transmissions. An investigation for an apodized occulter with manufacturing defaults is quickly performed. Conclusions. It has been possible to numerically demonstrate the large superiority of apodized circular occulters with respect to the sharp-edged ones. These occulters allow the theoretical observation of the very limb-close corona with not yet obtained contrast ratios.

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Section: Discussionmentioning

confidence: 99%

Theoretical performance of solar coronagraphs using sharp-edged or apodized circular external occulters

Aime

2013

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“…In Optics, this effect can be obtained with appropriate modifications of the pupil function. A large review of apodization techniques was made by Jacquinot & Roizen-Dossier (1964). These authors also suggested to illuminate the pupil with an interference pattern in a spectroscopic system for better slit illumination, but they abandoned the idea.…”

Section: Interferometric Apodization Of Rectangular Aperturesmentioning

confidence: 99%

Interferometric apodization of rectangular apertures

Aime¹,

Soummer²,

Ferrari³

2001

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Abstract. We describe the principle of an apodization technique for rectangular apertures that can be implemented using a Michelson or a Mach-Zender interferometer. Using several interferometers, any integer power of cosine functions can be obtained. The technique is considered for application to the Apodized Square Aperture (ASA) concept recently proposed by Nisenson & Papaliolios (2001). Simple analytic expressions for the Point Spread Functions of such apodized apertures are given. For a cosine to the power N apodization, the resulting focal plane amplitude is simply the sum of N + 1 weighted and shifted sine cardinal functions. The interest of such apodized apertures for coronagraphy is investigated. It appears that these apodization functions are very efficient provided that only a central part of the cosine-arch is used. Analytic expressions are derived for the residual amplitude left in an image of the aperture after the coronagraphic experiment. Best results are obtained with a cosine squared apodization.

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“…A binary design using a halftone-dot process can in principle be generalized to any apodizer masks (APLC, Dual zone) and even a conventional pupil apodization coronagraph (Jacquinot & Roisin-Dossier 1964;Nisenson & Papaliolios 2001;Aime 2005), or as an alternative manufacturing solution for binaryshaped pupil-coronagraph masks Kasdin et al 2003;Vanderbei et al 2004;Enya et al 2007Enya et al , 2008.…”

Section: Introductionmentioning

confidence: 99%

Design, analysis, and testing of a microdot apodizer for the Apodized Pupil Lyot Coronagraph

Martínez

Dorrer

Carpentier³

et al. 2008

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Context. Coronagraphic techniques are required for detecting exoplanets with future Extremely Large Telescopes. One concept, the Apodized Pupil Lyot Coronagraph (APLC), combines an apodizer in the entrance aperture with a Lyot opaque mask in the focal plane. This paper presents the manufacturing and testing of a microdots apodizer optimized for the near IR. Aims. We attempt to demonstrate the feasibility and performance of binary apodizers for the APLC. This study is also relevant to coronagraph using amplitude pupil apodization. Methods. A binary apodizer was designed using a halftone-dot process, where the binary array of pixels with either 0% or 100% transmission was calculated to fit the required continuous transmission, i.e. local transmission control was obtained by varying the relative density of the opaque and transparent pixels. An error-diffusion algorithm was used to optimize the distribution of pixels that approximated the required field transmission. The prototype was tested with a coronagraphic setup in the near IR. Results. The transmission profile of the prototype agrees with the theoretical shape to within 3% and is achromatic. The observed apodized and coronagraphic images are consistent with theory. However, binary apodizers introduce high frequency noise that is a function of the pixel size. Numerical simulations were used to specify pixel size and minimize this effect, and validated by experiment. Conclusions. This paper demonstrates that binary apodizers are well suited for use in high-contrast imaging coronagraphs. The correct choice of pixel size is important and must be addressed by considering the scientific field of view.

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II Apodisation

Cited by 175 publications

References 32 publications

Theoretical performance of solar coronagraphs using sharp-edged or apodized circular external occulters

Theoretical performance of solar coronagraphs using sharp-edged or apodized circular external occulters

Interferometric apodization of rectangular apertures

Design, analysis, and testing of a microdot apodizer for the Apodized Pupil Lyot Coronagraph

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