Requirements on optical density and phase dispersion of imperfect band-limited occulting masks in a broadband coronagraph

Sidick, Erkin

doi:10.1364/ao.46.007485

Cited by 6 publications

(4 citation statements)

References 7 publications

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“…In addition, all of the broadband contrast numbers presented here are dominated by the variations of occulter phase with wavelength inherent in HEBS glass profiles. Occulting profiles created by variable-thickness metallic coatings, for example, have very different phase behavior than HEBS, and in many cases achieve much better broadband contrasts [10][11][12][13].…”

Section: Resultsmentioning

confidence: 99%

Optimizing the broadband performance of TPF's high-contrast imaging testbed through modeling and simulations

2007

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We have carried out some investigation to optimize the broadband performance of the high-contrast imaging testbed (HCIT) at JPL through optical modeling and simulations. The analytical tool is an optical simulation algorithm developed by combining the HCIT's optical model with a speckle-nulling algorithm that operates directly on coronagraphic images, an algorithm very similar to the one that has been used on the HCIT. We have experimented in our simulations with different designs for the occulting mask and the Lyot Stop, and also tried several different specklenulling approaches. Some results predicted by our simulations agree well with the results measured on the HCIT. In this paper we describe the details of our simulations and present our results.

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Section: Resultsmentioning

confidence: 99%

Optimizing the broadband performance of TPF's high-contrast imaging testbed through modeling and simulations

2007

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“…Because the phases of these masks are ideally zero at λ = λ 0 , it is not necessary to carry out a speckle-nulling optimization when the HCIT is free of any other surface error. Our simulation has predicted that an error-free HCIT has the monochromatic contrast floors of C m = 1.65x10 -14 and C 4 = 3.76x10 -15 , respectively [13]. When the HCIT utilizes such a PMMA-corrected occulter, the occulter's OD and phase dispersions will come into play when the input beam is a broadband light and degrades the HCIT's broadband contrast performance.…”

Section: Corrected Masksmentioning

confidence: 92%

Effects of optical-density and phase dispersion of an imperfect band-limited occulting mask on the broadband performance of a TPF coronagraph

Sidick

Balasubramanian

2007

SPIE Proceedings

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Practical image-plane occulting masks required by high-contrast imaging systems such as the TPF-Coronagraph introduce phase errors into the transmitting beam, or, equivalently, diffract the residual starlight into the area of the final image plane used for detecting exo-planets. Our group at JPL has recently proposed spatially profiled metal masks that can be designed to have zero parasitic phases at the center wavelength of the incoming broadband light with small amounts of OD and phase dispersions at other wavelengths. Work is currently underway to design, fabricate and characterize such image-plane masks. In order to gain some understanding on the behaviors of these new imperfect band-limited occulting masks and clarify how such masks utilizing different metals or alloys compare with each other, we carried out some modeling and simulations on the contrast performance of the high-contrast imaging testbed (HCIT) at JPL. In this paper we describe the details of our simulations and present our results.

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“…The chromaticity of the apodizer is now related to the chromatic variation of the complex refractive index of the material. Solutions based on metallic thin film, alloy layer or else High-Energy Beam Sensitive (HEBS) glass have already been investigated to produce achromatic band-limited masks in the visible (Sidick 2007;Moody et al 2008;Balasubramanian 2008) or manufacture achromatic apodizers of the APLC coronagraph for VLT-SPHERE (Guerri et al 2008(Guerri et al , 2011Carbillet et al 2011) and Gemini Planet Imager (Soummer et al 2009;Sivaramakrishnan et al 2009). Our study is focused here on the search of metals to design chromatic components instead of grey masks.…”

Section: Design Proposal For the Colored Apodizationmentioning

confidence: 99%

Improved achromatization of phase mask coronagraphs using colored apodization

N’Diaye¹,

Dohlen²,

Cuevas³

et al. 2012

A&A

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Context. For direct imaging of exoplanets, a stellar coronagraph helps to remove the image of an observed bright star by attenuating the diffraction effects caused by the telescope aperture of diameter D. The Dual Zone Phase Mask (DZPM) coronagraph constitutes a promising concept since it theoretically offers a small inner working angle (IWA ∼ λ 0 /D where λ 0 denotes the central wavelength of the spectral range ∆λ), good achromaticity and high starlight rejection, typically reaching a 10 6 contrast at 5 λ 0 /D from the star over a spectral bandwidth ∆λ/λ 0 of 25% (similar to H-band). This last value proves to be encouraging for broadband imaging of young and warm Jupiter-like planets. Aims. Contrast levels higher than 10 6 are however required for the observation of older and/or less massive companions over a finite spectral bandwidth. An achromatization improvement of the DZPM coronagraph is therefore mandatory to reach such performance. Methods. In its design, the DZPM coronagraph uses a grey (or achromatic) apodization. We propose to replace it by a colored apodization to increase the performance of this coronagraphic system over a large spectral range. This innovative concept, called Colored Apodizer Phase Mask (CAPM) coronagraph, is defined with some design parameters optimized to reach the best contrast in the exoplanet search area. Once this done, we study the performance of the CAPM coronagraph in the presence of different errors to evaluate the sensitivity of our concept. Results. A 2.5 mag contrast gain is estimated from the performance provided by the CAPM coronagraph with respect to that of the DZPM coronagraph. A 2.2 · 10 −8 intensity level at 5 λ 0 /D separation is then theoretically achieved with the CAPM coronagraph in the presence of a clear circular aperture and a 25% bandwidth. In addition, our studies show that our concept is less sensitive to low than high-order aberrations for a given value of rms wavefront errors.

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Requirements on optical density and phase dispersion of imperfect band-limited occulting masks in a broadband coronagraph

Cited by 6 publications

References 7 publications

Optimizing the broadband performance of TPF's high-contrast imaging testbed through modeling and simulations

Optimizing the broadband performance of TPF's high-contrast imaging testbed through modeling and simulations

Effects of optical-density and phase dispersion of an imperfect band-limited occulting mask on the broadband performance of a TPF coronagraph

Improved achromatization of phase mask coronagraphs using colored apodization

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