Focal-plane wavefront sensing for segmented telescope

Delavaquerie, Enguerran; Cassaing, F.; Amans, Jean-Philippe

doi:10.1051/ao4elt/201005018

Cited by 5 publications

(2 citation statements)

References 13 publications

(14 reference statements)

Supporting

Mentioning

Contrasting

Order By: Relevance

“…The recovery of the segment misalignment can be directly obtained from the information in the image plane (Lofdahl et al 1998;Delavaquerie et al 2010;Martinache 2013;Pope et al 2014;Janin-Potiron et al 2016), in a pupil plane (e.g., Chanan 1989;Montoya-Martinez 2004;Esposito et al 2005;Dohlen et al 2006;Mazzoleni et al 2008;Pinna et al 2008), or in intermediate planes (e.g., Chanan et al 1999;Cuevas et al 2000;Chueca et al 2008). Image plane techniques are advantageous especially for space applications since they require a limited amount of hardware.…”

Section: Introductionmentioning

confidence: 99%

Fine cophasing of segmented aperture telescopes with ZELDA, a Zernike wavefront sensor in the diffraction-limited regime

Janin-Potiron

N’Diaye

Martínez

et al. 2017

A&A

View full text Add to dashboard Cite

Context. Segmented aperture telescopes require an alignment procedure with successive steps from coarse alignment to monitoring process in order to provide very high optical quality images for stringent science operations such as exoplanet imaging. The final step, referred to as fine phasing, calls for a high sensitivity wavefront sensing and control system in a diffraction-limited regime to achieve segment alignment with nanometric accuracy. In this context, Zernike wavefront sensors represent promising options for such a calibration. A concept called the Zernike unit for segment phasing (ZEUS) was previously developed for ground-based applications to operate under seeing-limited images. Such a concept is, however, not suitable for fine cophasing with diffraction-limited images. Aims. We revisit ZELDA, a Zernike sensor that was developed for the measurement of residual aberrations in exoplanet direct imagers, to measure segment piston, tip, and tilt in the diffraction-limited regime. Methods. We introduce a novel analysis scheme of the sensor signal that relies on piston, tip, and tilt estimators for each segment, and provide probabilistic insights to predict the success of a closed-loop correction as a function of the initial wavefront error. Results. The sensor unambiguously and simultaneously retrieves segment piston and tip-tilt misalignment. Our scheme allows for correction of these errors in closed-loop operation down to nearly zero residuals in a few iterations. This sensor also shows low sensitivity to misalignment of its parts and high ability for operation with a relatively bright natural guide star. Conclusions. Our cophasing sensor relies on existing mask technologies that make the concept already available for segmented apertures in future space missions.

show abstract

Section: Introductionmentioning

confidence: 99%

Fine cophasing of segmented aperture telescopes with ZELDA, a Zernike wavefront sensor in the diffraction-limited regime

Janin-Potiron

N’Diaye

Martínez

et al. 2017

A&A

View full text Add to dashboard Cite

show abstract

“…Cophasing methods can be divided into three flavors: (1) pupil plane techniques, such as the modified Shack-Hartmann (e.g., Chanan 1989;Chanan et al 2000a;Mazzoleni et al 2008), the Mach-Zehnder interferometer Yaitskova et al 2004Yaitskova et al , 2005, and avatars (Dohlen et al 2006;Surdej 2011); (2) intermediate plane techniques such as the curvature sensor (e.g., Chanan et al 1999;Cuevas et al 2000;Chueca et al 2008);and (3) focal plane techniques such as the phase diversity (Lofdahl et al 1998;Delavaquerie et al 2010), Pyramid sensor (Esposito et al 2005;Pinna et al 2008). More recent and peculiar approaches have been investigated using pupil asymmetry (asymmetric pupil wavefront sensor, Martinache 2013; Pope et al 2014) or differential optical transfer functions (Codona & Doble 2015).…”

Section: Introductionmentioning

confidence: 99%

The self-coherent camera as a focal plane fine phasing sensor

Janin-Potiron

Martínez

Baudoz

et al. 2016

A&A

View full text Add to dashboard Cite

Context. Direct imaging of Earth-like exoplanets requires very high contrast imaging capability and high angular resolution. Primary mirror segmentation is a key technological solution for large-aperture telescopes because it opens the path toward significantly increasing the angular resolution. The segments are kept aligned by an active optics system that must reduce segment misalignments below tens of nm rms to achieve the high optical quality required for astronomical science programs. Aims. The development of cophasing techniques is mandatory for the next generation of space-and ground-based segmented telescopes, which both share the need for increasing spatial resolution. We propose a new focal plane cophasing sensor that exploits the scientific image of a coronagraphic instrument to retrieve simultaneously piston and tip-tilt misalignments. Methods. The self-coherent camera phasing sensor (SCC-PS) adequately combines the SCC properties to segmented telescope architectures with adapted segment misalignment estimators and image processing. An overview of the system architecture, and a thorough performance and sensitivity analysis, including a closed-loop efficiency, are presented by means of numerical simulations. Results. The SCC-PS estimates simultaneously piston and tip-tilt misalignments and corrects them in closed-loop operation in a few iterations. As opposed to numerous phasing sensor concepts the SCC-PS does not require any a priori on the signal at the segment boundaries or any dedicated optical path. We show that the SCC-PS has a moderate sensitivity to misalignments, virtually none to pupil shear, and is by principle insensitive to segment gaps and edge effects. Primary mirror phasing can be achieved with a relatively bright natural guide star with the SCC-PS. Conclusions. The SCC-PS is a noninvasive concept and an efficient phasing sensor from the image domain. It is an attractive candidate for segment cophasing at the instrument level or alternatively at the telescope level, as usually envisioned in current space-and groundbased observatories.

show abstract