Interferometric apodization of telescope apertures

Carlotti, Alexis; Ricort, G.; Aime, Claude; Azhari, Y. El; Soummer, Rémi

doi:10.1051/0004-6361:20078270

Cited by 10 publications

(16 citation statements)

References 24 publications

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“…This is illustrated in Figure 1 in the case of an apodizer with central obstruction, where the apodizer corresponds to a different prolate function for each wavelength. This effect could be achieved for example using interferometry (Carlotti et al 2008) or approximated using a colored absorbing glass (Soummer et al 2006). In the case of a telescope with central obstruction, these ideal solutions would be very challenging to reproduce in practice because the position of the maximum transmission depends on the wavelength.…”

Section: Broadband Performance Achromatic Aplcsmentioning

confidence: 99%

Apodized Pupil Lyot Coronagraphs for Arbitrary Apertures. Iii. Quasi-Achromatic Solutions

Soummer

Sivaramakrishnan

Pueyo

et al. 2011

ApJ

107

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Direct imaging and spectroscopy of young giant planets from the ground requires broadband starlight suppression with coronagraphy. It is important to minimize the coronagraph chromatic sensitivity to help remove residual speckles through post-processing of images at multiple wavelengths. The coronagraph must also be able to mitigate the effects of ground-based telescopes with central obstruction. We present new properties of the Apodized Pupil Lyot Coronagraph (APLC) that enable quasi-achromatic starlight suppression over a broad bandpass (20%) and with central obstructions. We discuss the existence of these quasi-achromatic solutions using the properties of the generalized prolate spheroidal functions, which are used to define the apodizer profile. We discuss a broadband optimization method and illustrate its parameter space in terms of inner working angle and contrast. These new APLC solutions are implemented in the Gemini Planet Imager (GPI), a new facility instrument to detect and characterize young giant planets and disks, which will be commissioned in 2011. The coronagraph design delivers a contrast better than 10 −7 beyond a separation of 0.2 arcsec in the presence of Gemini's central obstruction over a 20% bandpass. The science camera is an integral field spectrograph observing in one of the Y, J, or H, or in about two-thirds of the K bandpass, at a single time. Similar solutions have also been used for the Palomar 1640 coronagraphic integral field spectrograph.

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Section: Broadband Performance Achromatic Aplcsmentioning

confidence: 99%

Apodized Pupil Lyot Coronagraphs for Arbitrary Apertures. Iii. Quasi-Achromatic Solutions

Soummer

Sivaramakrishnan

Pueyo

et al. 2011

ApJ

107

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“…First estimates for such a system (which will be presented in a forthcoming publication) indicate that this latter solution would not significantly reduce the integrated leakage, but apodization would contribute to reduce the stellar leakage at the level of the planet. A complex system would be to take advantage of the MZI by applying both the present technique and the phase apodization technique described in Carlotti et al (2008).…”

Section: Resultsmentioning

confidence: 99%

“…To achieve the nulling, ARC directly uses the dark fringe of the MZI, while AIC must darken the white fringe of the MI by inserting an achromatic π phase shift in one arm. This dark fringe property of the MZI of behaving like a subtractive device was applied in Aime et al (2007) and Carlotti et al (2008Carlotti et al ( , 2009. For an on-axis point source the achromatic nulling property for AIC and ARC is similar.…”

Section: Basic Principle Of Arcmentioning

confidence: 99%

“…Because of the field rotators, the respective complex amplitude distributions in the image plane are rotated one with respect to the other. The combination of refraction and reflection indices by the beamsplitters and its effects were described by Carlotti et al (2008). As discussed there, a MZI can be a perfect subtractor, if the beam splitter coefficients r BS and t BS are equal.…”

Section: Basic Equations In Cartesian Coordinates: Focal Plane Imagesmentioning

confidence: 99%

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ARC: an Achromatic Rotation-shearing Coronagraph

Aime¹,

Ricort²,

Carlotti

et al. 2010

A&A

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Context. Because of the larger size of future telescopes, the star leakage effect due to the finite diameter of the stars will become a major problem for coronagraphs with very small inner working angles (IWA). Aims. To reduce this star leakage, we propose a new instrumental concept, the Achromatic Rotation-shearing Coronagraph (ARC), that provides a variable IWA that is easily tunable to ensure the observation of Solar-like systems with an extremely large telescope. Methods. The ARC belongs to the nuller class of coronagraphs. It takes advantage of the achromatic dark output of a Mach-Zehnder interferometer (MZI). Field rotators set in the arms of the MZI rotate the π-phase shifted images of the MZI by an angle ψ. An on-axis point source (the star) is nulled as twin-images of an off-axis point source (the planet) are formed. For ψ = π, the ARC is equivalent to the achromatic interfero-coronagraph. For small ψ, the twin images of the off-axis source are formed close to each another, and eventually nulled if too close. In this way, the ARC can get rid of star leakage while optimizing the transmission of the planet. We describe the compensation of polarization effects induced by field rotators. An application to diluted apertures is shortly presented. Results. We perform the mathematical analysis of the technique using Cartesian and polar coordinates, and assuming that the system is optically perfect. Analytic expressions are given for the leakage in both the focal and aperture planes. Simplified expressions for the contrast and signal-to-noise ratio (SNR) in the focal plane are given for a circular aperture, explicitly showing that the level of star leakage decreases as sin 2 (ψ/2), while the SNR increases as the inverse of sin(ψ/2). Conclusions. The ARC is appropriate for the detection of exoplanets and is not intended to provide images of the environment of stars.

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“…The optical setup is a new version of the experiment used by Carlotti et al (2008) for interferometric apodization of telescope apertures, and where the ability of the MZI to work as an addition-subtraction instrument was described. A few general improvements were made, among them a piezoelectric remote control of the optical mounts of the mirrors and a stabilization of the temperature of the working environment.…”

Section: Optical Setup Of the Experimentsmentioning

confidence: 99%

Phase mask coronagraphy using a Mach-Zehnder interferometer

Carlotti

Ricort²,

Aime³

2009

A&A

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Aims. We report results obtained with a four-quadrant and an eight-octant phase-mask coronagraphs (4QC and 8OC) produced using amplitude masks inside a Mach-Zehnder interferometer (MZI). We describe the laboratory implementation of these coronagraphs operated in laser light and provide a detailed comparison between theory and experiment. Methods. The +1 and -1 (π phase) amplitude transmissions required to produce a 4QC or an 8OC were obtained using complementary binary-masks (transmission of 1 or 0 for quadrants of similar parities) in the two arms of a MZI, taking advantage of the achromatic π phase shift between the two paths. In one output of the MZI, the reconstructed image of the focal plane is similar to those obtained for sectorised phase-masks coronagraphs, and the image of the aperture corresponds to the characteristic patterns of the 4QC/8OC coronagraphs. Results. Observations are compared with the theory published by other authors and developed further here. The expressions for the light diffracted outside the aperture image are simplified using the Zernike radial polynomials Z 1 n instead of the rapidly diverging hypergeometric functions otherwise used. Experimental results are found to be in very good agreement with the theory. With the present laboratory experiment, about 99% of the light is rejected outside the Lyot stop and the contrast obtained beyond 5λ/D is higher than 10 5 for both the 4QC and 8OC. As expected, the 8OC is less affected by a pointing error than the 4QC, but more sensitive to an aperture central obstruction. Incidently, the loss of transmission for a planet crossing two phase masks is given theoretically as a function of the Lyot stop size, in agreement with observations.

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Interferometric apodization of telescope apertures

Cited by 10 publications

References 24 publications

Apodized Pupil Lyot Coronagraphs for Arbitrary Apertures. Iii. Quasi-Achromatic Solutions

Apodized Pupil Lyot Coronagraphs for Arbitrary Apertures. Iii. Quasi-Achromatic Solutions

ARC: an Achromatic Rotation-shearing Coronagraph

Phase mask coronagraphy using a Mach-Zehnder interferometer

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