Optimization of starshades: focal plane versus pupil plane

Flamary, Rémi; Aime, Claude

doi:10.1051/0004-6361/201423680

Cited by 6 publications

(4 citation statements)

References 23 publications

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“…Sensitive analysis of this particular stray light is rather complex as it includes an extended light source -the Sun -which makes such a work much more difficult than considering one single point source, as is done in the particular domain of exoplanet coronagraphy where numerous analytic studies have been done -see for instance (Cash 2006;Vanderbei et al 2007;Flamary et al 2014). In solar coronagraphy, only a few numerical and analytical studies of rejection performance have been published (Lenskii 1981;Aime et al 2002;Aime 2007Aime , 2013.…”

Section: Introductionmentioning

confidence: 99%

Performance of the hybrid externally occultedLyotsolar coronagraph

Rougeot

Flamary

Galano

et al. 2017

A&A

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Context. High-contrast hybrid coronagraphs, which combine an external occulter and a Lyot-style coronagraph became a reality in recent years, despite the lack of analytic and numerical end-to-end performance studies. The solar coronagraph ASPIICS which will fly on the future ESA Formation Flying mission Proba-3 is a good example of such a hybrid coronograph. Aims. We aim to provide a numerical model to compute theoretical performance of the hybrid externally occulted Lyot-style coronagraph, which we then aim to compare to the performance of the classical Lyot coronagraph and the externally occulted solar coronagraph. We will provide the level and intensity distribution of the stray light, when the Sun is considered as an extended source. We also investigate the effect of different sizes for the internal occulter and Lyot stop. Methods. First, we have built on a recently published approach, to express the diffracted wave front from Fresnel diffraction produced by an external occulter at the entrance aperture of the coronagraph. Second, we computed the coherent propagation of the wave front coming from a given point of the Sun through the instrument. This is performed in three steps: from the aperture to the image of the external occulter, where the internal occulter is set, from this plane to the image of the entrance aperture, where the Lyot stop is set, and from there to the final image plane. Making use of the axis-symmetry, we considered wave fronts originating from one radius of the Sun and we circularly average the intensities. Our numerical computation used the parameters of ASPIICS. Results. The hybrid externally occulted Lyot coronagraph rejects sunlight below 10 −8 B from 1.3 R -in the particular configuration of ASPIICS. The Lyot coronagraph effectively complements the external occultation. We show that reducing the Lyot stop allows a clear gain in rejection, being even better than oversizing the internal occulter, that tends to exclude observations very close to the solar limb. As an illustration, we provide a graph that allows us to estimate performance as a function of the internal occulter and Lyot stop sizes. Conclusions. Our work consists of a methodological approach to compute the end-to-end performance for solar coronagraph.

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Section: Introductionmentioning

confidence: 99%

Performance of the hybrid externally occultedLyotsolar coronagraph

Rougeot

Flamary

Galano

et al. 2017

A&A

Self Cite

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“…The same problem of an evanescent PSF arises, in a rather complex manner. In this case, the shaped occulters have a low number of petals (for example 20 in the computation of Cady ( 2012)) with a particularly studied profile to obtain a very dark shadow, Vanderbei et al (2007), Flamary & Aime (2014). These occulters are typically of tens of meters to tens of thousands of kilometers in front of a telescope of a few meters in diameters (see Arenberg et al (2021) for a very pedagogic discussion of this issue).…”

Section: Inverse Fredholm Reconstruction For Exoplanet Imaging Using ...mentioning

confidence: 99%

Simulation of inverse Fredholm reconstruction in a vignetting zone: application to ASPIICS

Theys

Aimé

Rougeot

et al. 2022

A&A

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Aims. This work deals with image reconstruction in a vignetting zone where the point spread function (PSF) becomes evanescent and the image undergoes a Fredholm transformation. The application of this method is aimed at the reconstruction of the solar corona in the vignetting zone of the ASPIICS coronagraph. It extends on a previous paper in several aspects. Methods. We used a matrix formalism for the exact inversion of the Fredholm integral. The stray light appears there as a bias. We performed two procedures: either the direct processing of the biased data or their processing following the subtraction of the bias. In the first case, the statistics follow a Poisson distribution and a Kullback-Leibler divergence was used; in the second case, we were led to use a simplifying Gaussian statistic. In both cases, a physical regularization using a Strehl criterion was implemented and this improved the results. Image reconstruction in the vignetting area is done in the case of a perfect coronagraph for two diameters of the internal occulter, but also in the case of formation flight errors and optical defects that are present but ignored by the inversion procedure.Results. Poisson and Gauss models both give much better results than simple flux compensation. For the Poisson model, unexpected pseudo-fringes are present in the reconstructed raw image but are greatly reduced using regularization. The Gaussian model (using de-biased data) is found to give better results, no matter whether it is the regularized or non-regularized version of the algorithm that is used. Despite a high level of stray light, the internal occulter of a smaller dimension allows us to approach much closer to the solar edge without too great a loss in terms of quality in the outer regions. This conclusion remains true in the case of optical micro-defects leading to speckles in the PSF because that has only a slight impact on the images in the vignetting area. In the case of formation flying errors, the Fredholm inversion is more affected by these for the small internal occulter than for the larger one. Conclusions. The method proposed for the Fredholm inversion is general and can be transposed to other systems using external occulters. An application of this method to the imaging of exoplanets is generally envisaged.

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“…Urania: As starshades are a relatively new technology, there are many exciting research problems prime for exploration. First, there has not been much progress on the optimization of the apodization function for many years 14,93,94 and surely there is a room for improvement; perhaps this could lead to the design of smaller, closer-in starshades.…”

Section: Day 4: Starshade Programmaticsmentioning

confidence: 99%

Special Section on Starshades: Overview and a Dialogue

Arenberg

Harness

Jensen-Clem

2021

J. Astron. Telesc. Instrum. Syst.

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This special section is dedicated to starshades: science, engineering, technology, and programmatics. Our reasons for organizing this special section are several fold. First as a new technology and with research accomplished in many institutions, recent results are widely scattered in the literature. As such, we see great value in colocating many of the most recent results. This guest editorial summarizes the 19 contributed papers as the result of a special call for papers. Since this is a rapidly maturing technology, we wanted to colocate a primer with the most current work in the field. It is hoped that this primer will provide a tutorial to the starshade concept and pathway to the literature not in this section. In doing so, we hope to widen the starshade community in terms of engineering and scientific engagements. This tutorial takes the form of a dialogue, where frequently asked questions are answered.

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Optimization of starshades: focal plane versus pupil plane

Cited by 6 publications

References 23 publications

Performance of the hybrid externally occultedLyotsolar coronagraph

Performance of the hybrid externally occultedLyotsolar coronagraph

Simulation of inverse Fredholm reconstruction in a vignetting zone: application to ASPIICS

Special Section on Starshades: Overview and a Dialogue

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