DICOS is a technological demonstrator under a stratospheric balloon for advanced pointing and wavefront stability technologies. The aim is to reach 10 mas fine pointing and 20 nm rms wavefront error (WFE), with 1 nm rms stability. The sizing case comes from the coronography technique for exoplanets direct detection. The instrument is based on a 40 cm telescope made in aluminum and mounted in a CARMEN gondola. The deformations and pointing errors are compensated by active loops driving a deformable mirror (DM) with 97 actuators. The current funded phase of the project will end in 2024 by a full-scale ground demonstration.

DICOS: a demonstrator of advanced active optics and fine pointing techniques for future space-based missions

The SPEED project aims at developing and testing key recipes for high-contrast imaging at small angular separations with unfriendly telescope apertures. SPEED combines optimized segmented aperture coronagraphy, dual-deformable mirrors wavefront control and shaping architecture for creating a dark hole in the scientific image by deformable mirror (DM) actuation. The challenge is to overcome the various fundamental limitations for quasi-static speckle calibration at very small angular separations. We report on the progress made in elaborating an accurate simulated model of our instrument in preparation for the wavefront control and wavefront shaping strategy with a multi-DM setup.

Gearing up the SPEED wavefront shaping strategy

The segmented pupil experiment for exoplanet detection (SPEED) facility aims to improve knowledge and insight into various areas required for gearing up high-contrast imaging instruments adapted to the unprecedented high angular resolution and complexity of the forthcoming extremely large telescopes (ELTs). SPEED combines an ELT simulator, cophasing optics, wavefront control and shaping with a multi-deformable mirror (DM) system, and optimized small inner-working angle (IWA) coronagraphy. The fundamental objective of the SPEED setup is to demonstrate deep contrast into a dark hole optimized for small field of view and very small IWA, adapted to the hunt of exoplanets in the habitable zone around late-type stars. SPEED is designed to implement an optimized small IWA coronagraph: the phase-induced amplitude apodization complex mask coronagraph (PIAACMC). The PIAACMC consists in a multi-zone phase-shifting focal plane mask (FPM) and two apodization mirrors (PIAA-M1 and PIAA-M2), with strong manufacturing specifications. Recently, a first-generation prototype of a PIAACMC optimized for the SPEED facility has been designed and manufactured. The manufacturing components exhibit high optical quality that meets specifications. In this paper, we present how these components have been characterized by a metrological instrument, an interferential microscope, and then we show what is yielded from this characterization for the FPM and the mirrors. Eventually, we discuss the results and the perspectives of the implementation of the PIAACMC components on the SPEED setup.

A metrological characterization of the SPEED test-bed PIAACMC components

Uncorrected wavefront errors create speckle noise in high-contrast observations at small inner-working angles. These speckles can be sensed and controlled by using coronagraph integrated wavefront sensors. Here, we will present how the Phase Induced Amplitude Apodized Complex Mask Corongraph (PIAACMC) can be integrated with both a Self-Coherent Camera (SCC) for focal plane wavefront sensing and an extremely sensitivity high-order pupil plane Zernike wavefront sensor (ZWFS). Non-common path aberrations can be completely erased by integrating both sensors into the PIAACMC, which is of extremely high importance in high-contrast imaging.

pdf/integrated-coronagraphy-and-wavefront-sensing-with-the-ejw67osqw3.pdf

Integrated coronagraphy and wavefront sensing with the PIAACMC

Context. The phase-induced amplitude apodization complex mask coronagraph (PIAACMC) is a coronagraph architecture for the direct detection of extrasolar planets. The PIAACMC can achieve close to the theoretical performance limit at small angular separations. The concept is a high-performance PIAA-based coronagraph that is su ﬃ ciently versatile to be designed for next-generation segmented and obscured telescope apertures. Aims. We present key elements of the design and manufacture of a PIAACMC for the segmented pupil experiment for exoplanet detection (SPEED) testbed. The primary components of a PIAACMC system are the PIAA optics and the complex phase-shifting focal plane mask (FPM). The most challenging part of the system to model is the error on the manufacturing of the two PIAA mirrors. Methods. In this paper, we describe the design and manufacturing of the FPM and moderate-sag PIAA optics using photolithography and etching. We present the design and fabrication of the PIAACMC, along with metrology, and an initial assessment of the PIAACMC optics e ﬃ ciency. Results. Errors in the fabricated component proﬁles degrade the overall performance. We show that the depth errors involved are of a few tens of nanometers and a few hundred nanometers for the FPM and PIAA optics, respectively. The metrological and individual performance analysis of the FPM and PIAA optics provides us with an in-depth understanding of these optical quality of the components, manufacturing error propagation, and the e ﬀ ects of these on performance. Because the deformable mirror (DM) location is critical in a PIAA system, we show that despite the pupil remapping e ﬀ ect of the PIAA optics, a dual-DM wavefront control and shaping system architecture optimized for short angular separations is operating adequately to compensate for manufacturing errors and for the dark zone generated in the focal plane. Conclusions. Because the errors involved are comparable to the wavefront error on the optics, wavefront control can compensate for them. Our measurements provide reliable models that, when used in simulations, allow us to reﬁne component speciﬁcation given the manufacturing errors at the raw coronagraphic performance level as well as after wavefront control and shaping.

Design, manufacturing, and testing of phase-induced amplitude apodization and phase-shifting optics for segmented telescopes

Context. High-contrast imaging of exoplanets around nearby stars with future large-segmented apertures requires starlight suppression systems optimized for complex aperture geometries. Future extremely large telescopes (ELTs) equipped with high-contrast instruments operating as close as possible to the diffraction limit will open a bulk of targets in the habitable zone around M-stars. In this context, the phase-induced amplitude apodization complex mask coronagraph (PIAACMC) is a promising concept for high-efficiency coronagraphic imaging at small angular separations with segmented telescopes.Aims. The complex focal plane mask of the PIAACMC is a multi-zone, phase-shifting mask comprised of tiled hexagons that vary in depth. The mask requires micro-fabrication techniques because it is generally made of hundreds micron-scale hexagonal zones with depths ranging over a few microns. We aim to demonstrate that the complex focal plane mask of a PIAACMC with a small inner working angle can be designed and manufactured for segmented apertures.Methods. We report on the numerical design, specifications, manufacturing, and characterization of a PIAACMC complex focal plane mask for the segmented pupil experiment for exoplanet detection facility.Results. Our PIAACMC design offers an inner working angle of 1.3 λ /D and is optimized for a 30% telescope-central-obscuration ratio including six secondary support structures (ESO/ELT design). The fabricated reflective focal plane mask is made of 499 hexagons, and the characteristic size of the mask features is 25 μ m, with depths ranging over ±0.4 μ m. The mask sag local deviation is measured to an average error of 3 nm and standard deviation of 6 nm rms. The metrological analysis of the mask using interferential microscopy gives access to an in-depth understanding of the component’s optical quality, including a complete mapping of the zone depth distribution zone-depth distribution. The amplitude of the errors in the fabricated mask are within the wavefront control dynamic range.Conclusions. We demonstrate the feasibility of fabricating and characterizing high-quality PIAA complex focal plane masks.

/pdf/design-and-manufacturing-of-a-multi-zone-phase-shifting-1eew2heomk.pdf

Design and manufacturing of a multi-zone phase-shifting coronagraph mask for extremely large telescopes

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Design and manufacturing of a multi-zone phase-shifting coronagraph mask for extremely large telescopes

A metrological characterization of the SPEED test-bed PIAACMC components

A metrological characterization of the SPEED test-bed PIAACMC components