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

Context. The major source of noise limiting high-contrast imaging is caused by quasi-static speckles. Speckle noise originates from wavefront errors caused by various independent sources, and evolves on different timescales depending on their nature. An understanding of how quasi-static speckles originate from instrumental errors is paramount to the search for faint stellar companions. Instrumental speckles average to form a fixed pattern, which can be calibrated to a certain extent, but their temporal evolution ultimately limits this possibility. Aims. This study focuses on the laboratory evidence and characterization of the quasi-static pinned speckle phenomenon. Specifically, we examine the coherent amplification of the static speckle contribution to the noise variance in the scientific image, through its interaction with quasi-static speckles. Methods. The analysis of a time series of adaptively corrected, coronagraphic images recorded in the laboratory enables the characterization of the temporal stability of the residual speckle pattern in both direct and differential coronagraphic images. Results. We estimate that spoiled and rapidly evolving quasi-static speckles present in the system at the angstrom/nanometer level affect the stability of the static speckle noise in the final image after the coronagraph. The temporal evolution of the quasi-static wavefront error exhibits a linear power law, which can be used to first order to model quasi-static speckle evolution in high-contrast imaging instruments.

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“…It is installed at an F/48 beam. Further details of the prototype can be found in Martinez et al (2009).…”

Section: Methodsmentioning

confidence: 99%

Speckle temporal stability in XAO coronagraphic images

Martínez

Loose

Carpentier

et al. 2012

A&A

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“…The main technical challenge in building an APLC is the apodizer. Prototypes are currently being developed using different approaches and tested to validate the concept in laboratory conditions (Boccaletti et al 2008;Martinez et al 2008b; Thomas et al 2008;Martinez et al 2009). …”

Section: Introductionmentioning

confidence: 99%

“…In a former study (Martinez et al 2009, hereafter Paper I), we explored a halftone-dot process to generate an array of binary pixels, either transparent or opaque, where the density of opaque pixels is spatially varying. This technique aims to solve the drawbacks of a continuous deposit of a metal layer with spatially varying thickness.…”

Section: Introductionmentioning

confidence: 99%

Design, analysis, and testing of a microdot apodizer for the apodized pupil Lyot coronagraph

Martínez¹,

Dorrer²,

Kasper³

et al. 2009

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Context. The Apodized Pupil Lyot Coronagraph (APLC) is a promising coronagraphic device for direct exoplanet detection with the European Extremely Large Telescope. This concept features amplitude apodization in the entrance aperture, and a small opaque Lyot mask in the focal plane. We present new near-IR laboratory results using binary apodizers -the so-called microdot apodizer -which represent a very attractive and advantageous solution for the APLC. Aims. Microdot apodizers introduce high-frequency noise whose characteristics depend on the pixel size. The aim of this work is to characterize the impact of the pixel size on the coronagraphic image. We aim to estimate both the noise intensity and its localization in the field of view. Methods. The microdot apodizer, consisting of an array of pixels with spatially variable density that are either opaque or transparent, was manufactured by lithography of a light-blocking metal layer deposited on a transparent substrate. A set of 5 masks has been designed with different pixel sizes, tested in the near-IR, and their behavior compared to theoretical models. Results. Stray light diffraction introduced by the finite pixel size was measured during experiments. The intensity decreases, and radial distance increases, when the pixel size gets smaller. Conclusions. The physical properties of these microdot apodizers have been demonstrated in the laboratory. The microdot apodizer is a suitable solution for any coronagraph using pupil amplitude apodization, if properly designed.

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“…Diffraction stray-light analysis and guidelines for the design of pupilapodized coronagraphs (e.g. apodized pupil Lyot coronagraph, dual zone coronagraph, conventional pupil-apodization concepts) are available in [1,2], while the specific case of focal-plane mask with a …”

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Halftoning for high-contrast imaging

Martínez

Dorrer

Carpentier

et al. 2011

EPJ Web of Conferences

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Abstract. High-contrast instruments, such as SPHERE (upcoming planet finder instrument for the ESO-VLT), or EPICS (planet hunter project for the future E-ELT), will require customized components with spatially varying transmission (e.g. coronagraphs, optical components that reduce the contrast between a companion and its parent star). The goal of these sub-systems is to control the spatial transmission, either in a pupil plane (pupil apodization), or in a focal plane of the instrument (occulting mask, i.e. lowfrequency filter). Reliably producing components with spatially varying transmission is not trivial, and different techniques have been already investigated for application to astronomy (e.g. metal deposition with spatially-varying thickness, or high-energy beam sensitive glass using e-beam lithography). We present some results related to the recent development of components with spatially varying transmission using a relatively simple technique analogous to the digital halftoning process used for printing applications. HALFTONE DOT PROCESS PRINCIPLEHalftoning has been used for hundreds of years in the printing industry as a solution for generating continuous-tone images with only black or white dots. The so-called halftone image, seen from a distance, should resemble the original continuous-tone image as much as possible, based on human vision perception. Following this idea, the continuous transmission of an optical filter can be generated with a specific implementation of opaque and transparent pixels as presented in Figure 1.The resulting microdot filter is an array of dots (i.e. pixels) that are either opaque (0% transmission) or transparent (100% transmission). It is fabricated by lithography of a light-blocking metal layer deposited on a transparent glass substrate. The technique has several advantages: relative ease of manufacturing, achromaticity, reproducibility, and ability to generate continuous and rapidly varying transmission functions, without introducing wavefront errors.Several application-dependent parameters must be carefully defined. Microdot filters are arrays of pixels with binary transmission, and light propagating through them has a continuously varying intensity after free-space propagation, or after filtering in the far field. Therefore, these filters have a power spectrum different from the power spectrum of an ideal continuous filter. The way dots are distributed, the size of the dots, and the density of the dots in the pattern directly impact the power spectrum of the filter, and these parameters must be carefully studied accordingly with the application. Several studies have been carried out to quantify diffraction effects induced by the pixellation and binary transmission of the pixels. Diffraction stray-light analysis and guidelines for the design of pupilapodized coronagraphs (e.g. apodized pupil Lyot coronagraph, dual zone coronagraph, conventional pupil-apodization concepts) are available in [1,2], while the specific case of focal-plane mask with a

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

Cited by 82 publications

References 18 publications

Speckle temporal stability in XAO coronagraphic images

Speckle temporal stability in XAO coronagraphic images

Design, analysis, and testing of a microdot apodizer for the apodized pupil Lyot coronagraph

Halftoning for high-contrast imaging

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