Study of a coronagraphic mask using evanescent waves

Buisset, Christophe; Rabbia, Yves; Lépine, Thierry; Alagao, Mary-Angelie; Ducrot, Elsa; Poshyachinda, S.; Soonthornthum, Boonrucksar

doi:10.1364/oe.25.007273

Cited by 11 publications

(7 citation statements)

References 11 publications

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“…(6) in Eq. (1) to get the structure function after AO correction, it is possible to get h and the long-exposure PSF induced by the residual fitting error, h , via Eq. (3).…”

Section: Analytical Model Of the Fitting Errormentioning

confidence: 99%

Inverse problem approach in Extreme Adaptive Optics: analytical model of the fitting error and lowering of the aliasing

Berdeu,

Tallon,

Thiébaut

et al. 2023

Preprint

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We present the results obtained with an end-to-end simulator of an Extreme Adaptive Optics (XAO) system control loop. It is used to predict its on-sky performances and to optimise the AO loop algorithms. It was first used to validate a novel analytical model of the fitting error, a limit due to the Deformable Mirror (DM) shape. Standard analytical models assume a sharp correction under the DM cutoff frequency, disregarding the transition between the AO corrected and turbulence dominated domains. Our model account for the influence function shape in this smooth transition. Then, it is well-known that Shack-Hartmann wavefront sensors (SH-WFS) have a limited spatial bandwidth, the high frequencies of the wavefront being seen as low frequencies. We show that this aliasing error can be partially compensated (both in terms of Strehl ratio and contrast) by adding priors on the turbulence statistics in the framework of an inverse problem approach. This represents an alternative to the standard additional optical filter used in XAO systems. In parallel to this numerical work, a bench was aligned to experimentally test the AO system and these new algorithms comprising a DM192 ALPAO deformable mirror and a 15×15 SH-WFS. We present the predicted performances of the AO loop based on end-to-end simulations.

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“…(6) in Eq. (1) to get the structure function after AO correction, it is possible to get h and the long-exposure PSF induced by the residual fitting error, h , via Eq. (3).…”

Section: Analytical Model Of the Fitting Errormentioning

confidence: 99%

Inverse problem approach in Extreme Adaptive Optics: analytical model of the fitting error and lowering of the aliasing

Berdeu,

Tallon,

Thiébaut

et al. 2023

Preprint

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“…In 2016, NARIT and IOGS/LabHC have developed a testbed to demonstrate the concept of EvWaCo. This testbed has been presented in previous communication [3][4] [5] and is similar to the schematic presented in Figure 1. The only difference is that the DM is replaced by a plane mirror.…”

Section: Evwaco Testbed Performancementioning

confidence: 99%

“…The focal plane mask (FPM) involves the frustration of total internal reflection [2] (FTIR) to suppress the central star light. We showed in the previous communication [3] that the mask has a quasi-Gaussian transmission and is achromatic such that its size varies linearly with wavelength.…”

Section: Introductionmentioning

confidence: 99%

“…The schematic of the proposed coronagraph is shown in Figure 1.The output beam coming from the telescope is collimated and is reflected by a deformable mirror (DM) toward the lens L1 that focuses the beam on the hypotenuse of the Focal Plane Mask FPM. This FPM is composed of a prism placed in contact with the convex diopter of a planoconvex lens [3]. On the star channel, the on-axis beam is transmitted by the FPM due to the frustration of the total internal reflection (FTIR).…”

Section: Introductionmentioning

confidence: 99%

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The evanescent wave coronagraph project: development status and potential for space based observations

Alagao

Buisset

Lépine³

et al. 2019

International Conference on Space Optics — ICSO 2018

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The Evanescent Wave Coronagraph (EvWaCo) is a coronagraph with an occulting mask based on the frustration of total internal reflection to i) produce an achromatic extinction of the central star and ii) reveal the faint companion surrounding the star. Results obtained in laboratory conditions show contrast performance of a few 10-6 between 10 λC/D and 20 λC/D over the full I-band centered at the wavelength λC = 800 nm with a spectral ratio of ∆λ/ λC ≈ 20% in unpolarized light. In this paper, we discuss the advantages of using EvWaCo to observe and characterize exoplanets with a space-based telescope. In the first section, we describe the system and present the current results obtained with the EvWaCo testbed. We also illustrate the capability of this coronagraph to detect the companion 30,000 times (respectively, 100,000 times) fainter than the central star at distances equal to 15 Airy radii (respectively, 30 Airy radii) from the PSF center in polychromatic and unpolarized light. In the second section, we describe the design of the prototype dedicated to the on-sky tests of the instrument with the 2.4 m Thai National Telescope at horizon 2020. This prototype has been designed with the objective to reach a contrast equal to a few 10-4 at the inner working angle (IWA) equal to 3 λ/D from the star PSF center while observing through the atmosphere over the full photometric I-band. This prototype will include an adaptive optics specified to reach at λ ≈ 800 nm a Strehl ratio > 0.8 for magnitude m < 7. In the third section, we show the theoretical performance of EvWaCo: a contrast comprised between a few 10-6 and 10-7 in the I-Band between 3 λ/D and 10 λ/D in the I-Band for an IWA equal to 3 λ/D with a Gaussian apodization in unpolarized light. We also show that similar contrasts performance are obtained in the V-, R-, bands, thus illustrating the EvWaCo quasi-achromaticity. Finally, we discuss the advantages and the limitation using the proposed concept for space-based observations and spectral characterization of exoplanets.

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“…Moreoever, the mask inherently adapts itself to the wavelength, thus, providing an achromatic rejection. [9][10][11] In this paper, we present the current status of this project. In particular, we describe the prototype that is currently in development and the performance of the coronagraph in the laboratory.…”

Section: Introductionmentioning

confidence: 99%

Design, performance, and potential scientific applications of the evanescent wave coronagraph with an adjustable inner working angle

Alagao

Buisset

Kawinkij

et al. 2021

International Conference on Space Optics — ICSO 2020

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The Center for Optics and Photonics of the National Astronomical Research Institute of Thailand, together with the Institut d'Optique Graduate School and the Centre de Recherche Astrohpysique de Lyon (CRAL), is currently developing the Evanescent Wave Coronagraph (EvWaCo). The coronagraph relies on the tunneling effect to produce a fully achromatic focal plane mask (FPM) with an adjustable size. The full instrument comprises a coronagraph and adaptive optics system that will be mounted on the Thai National Telescope and is specified to reach a raw contrast of 10 −4 at an inner working angle of 3 Airy radii. The coronagraph will be used to perform high contrast observations of stellar systems during on-sky observations over the spectral domain [600 nm, 900 nm]. In this paper, we present the opto-mechanical design of the EvWaCo prototype and the performance measured in laboratory conditions. We also discuss the potential applications for space-based observations and the development plan under this project in the next five years.

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Study of a coronagraphic mask using evanescent waves

Cited by 11 publications

References 11 publications

Inverse problem approach in Extreme Adaptive Optics: analytical model of the fitting error and lowering of the aliasing

Inverse problem approach in Extreme Adaptive Optics: analytical model of the fitting error and lowering of the aliasing

The evanescent wave coronagraph project: development status and potential for space based observations

Design, performance, and potential scientific applications of the evanescent wave coronagraph with an adjustable inner working angle

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