Co-phasing of a diluted aperture synthesis instrument for direct imaging: Experimental demonstration on a temporal hypertelescope

Bouyeron, Laurent; Delage, Laurent; Grossard, Ludovic; Reynaud, François

doi:10.1051/0004-6361/201117319

“…The faint companion is at least ten times brighter than the noise observed experimentally. The signalto-noise ratio value observed for 500 photons/frame reaches the limitation previously recorded with our co-phasing process using high flux data (Bouyeron et al 2012). This limitation is intrinsic to our test bench and is mainly due to the misalignment of the neutral axis of maintaining polarization fibre at each connection.…”

Section: Image Acquisition Of An Unbalanced Binary Star Systemsupporting

confidence: 82%

“…Obviously, the co-phasing quality is lower than this one, which was previously obtained in high flux level (i.e. 4 nm, see Bouyeron et al 2012), but as we see below, it is sufficient for acquiring high-contrast long-exposure images. …”

Section: Experimental Co-phasing Tests Of the Temporal Hypertelescopementioning

confidence: 76%

“…In a previous study using a high flux level (Bouyeron et al 2012), we numerically tested the co-phasing efficiency of each A87, page 4 of 8 6. Simulations of the dynamic range evolution DR s , computed from the short-exposure images as a function of the number of cycles in the photon-counting regime for various pairs in the metric-phase diversity range.…”

Section: Selection Of the Most Efficient Metricmentioning

confidence: 99%

“…This instrument consists of eight telescopes linked to an integrated-optics eight-to-one interferometer through optical fibres. In a previous step (Bouyeron et al 2012), we developed a co-phasing method based on a joint use of a genetic algorithm (GA, Brady 1985) and the sub-aperture piston phase diversity technique (SAPPD, Bolcar & Fienup 2005). This method relies on the use of the current image and an aberrated one in order to infer the instrument phase without any a priori knowledge on the observed object.…”

Section: Introductionmentioning

confidence: 99%

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Co-phasing of a diluted aperture synthesis instrument for direct imaging

Bouyeron¹,

Delage²,

Baudoin³

et al. 2014

A&A

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Context. Amongst the new techniques currently developed for high-resolution and high-dynamics imaging, the hypertelescope architecture is very promising for direct imaging of objects such as exoplanets. The performance of this instrument strongly depends on the co-phasing process accuracy. In a previous high-flux experimental study with an eight-telescope array, we successfully implemented a co-phasing system based on the joint use of a genetic algorithm and a sub-aperture piston phase diversity using the object itself as a source for metrology. Aims. To fit the astronomical context, we investigate the impact of photon noise on the co-phasing performance operating our laboratory prototype at low flux. This study provides experimental results on the sensitivity and the dynamics that could be reached for real astrophysical observations. Methods. Simulations were carried out to optimize the critical parameters to be applied in the co-phasing system running in the photon-counting regime. We used these parameters experimentally to acquire images with our temporal hypertelescope test bench for different photon flux levels. A data reduction method allows highly contrasted images to be extracted. Results. The optical path differences have been servo-controlled over one hour with an accuracy of 22.0 nm and 15.7 nm for 200 and 500 photons/frame, respectively. The data reduction greatly improves the signal-to-noise ratio and allows us to experimentally obtain highly contrasted images. The related normalized point spread function is characterized by a 1.1 × 10 −4 and 5.4 × 10 −5 intensity standard deviation over the dark field (for 15 000 snapshots with 200 and 500 photons/frame, respectively). Conclusions. This laboratory experiment demonstrates the potential of our hypertelescope concept, which could be directly transposed to a space-based telescope array. Assuming eight telescopes with a 30 cm diameter, the I-band limiting magnitude of the main star would be 7.3, allowing imaging of a companion with a 17.3 mag.

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“…Since described in Labeyrie 1996, the hypertelescope principle has been discussed by different authors (Tarmoul 2009;Lardiere et al 2007;Bouyeron et al 2012;Patru et al 2011;Aime et al 2012). Various optical architectures can be adopted, one of which is a N-aperture Fizeau interferometer equipped with a pupil densifier, typically a small or even micro-optical accessory which can fit near the focal camera.…”

Section: The Basic Optics Of Hypertelescopesmentioning

confidence: 99%

Hypertelescopes: The Challenge of Direct Imaging at High Resolution

Labeyrie

¹

2013

EAS Publications Series

5

0

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Sparse optical interferometric arrays of many apertures can produce direct images in the densified-pupil mode, also called "hypertelescope" mode. Pending the introduction of adaptive optics for cophasing, indirect images can also be reconstructed with speckle imaging techniques. But adaptive phasing is preferable, when a sufficiently bright guide star is available. Several wave sensing techniques, byproducts of those used on monolithic telescopes for some of them, are potentially usable. For cophased direct images of very faint sources in the absence of a natural guide star, a modified form of the Laser Guide Star techniques demonstrated on conventional and segmented telescopes is described. Preliminary testing in laboratory suggests further investigation. Recorded images, assumed co-phased, are also improvable post-detection with optical aperture-synthesis techniques such as Earth rotation synthesis, where data from successive exposures are combined incoherently. Nevertheless, the gain becomes modest if hundreds of sub-apertures are used. Image deconvolution techniques are also applicable, if suitably modified as demonstrated by Aime et al. (2012), and Mary (2012). Their modified deconvolution algorithms can extend the Direct Imaging Field (also called Clean Field) of hypertelescopes. More sub-apertures at given collecting area, implying that their size is reduced, improve the direct-imaging performance. The predictable trend thus favors systems combining hundreds of sub-apertures of modest size, if workable designs can be evolved. One such design, the "Ubaye Hypertelescope" entering the initial testing phase in the southern Alps, has a fixed spherical meta-mirror with a 57 m effective aperture, expandable to 200 m. Preliminary results suggest that larger versions, whether spherical or active paraboloidal, can reach a kilometric aperture size at terrestrial sites having a suitable concave topography. In space, hypertelescope meta-apertures spanning up to 100 000 km are in principle feasible in the form of a flotilla of mirrors, driven by micro-thrusters or by the radiation pressure of the Sun or lasers.

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Hypertelescopes: The Challenge of Direct Imaging at High Resolution

Labeyrie¹

2020

New Concepts in Imaging: Optical and Statistical Models

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Sparse optical interferometric arrays of many apertures can produce direct images in the densified-pupil mode, also called "hypertelescope" mode. Pending the introduction of adaptive optics for cophasing, indirect images can also be reconstructed with speckle imaging techniques. But adaptive phasing is preferable, when a sufficiently bright guide star is available. Several wave sensing techniques, byproducts of those used on monolithic telescopes for some of them, are potentially usable. For cophased direct images of very faint sources in the absence of a natural guide star, a modified form of the Laser Guide Star techniques demonstrated on conventional and segmented telescopes is described. Preliminary testing in laboratory suggests further investigation. Recorded images, assumed co-phased, are also improvable post-detection with optical aperture-synthesis techniques such as Earth rotation synthesis, where data from successive exposures are combined incoherently. Nevertheless, the gain becomes modest if hundreds of sub-apertures are used. Image deconvolution techniques are also applicable, if suitably modified as demonstrated by Aime et al. (2012), and Mary (2012). Their modified deconvolution algorithms can extend the Direct Imaging Field (also called Clean Field) of hypertelescopes. More sub-apertures at given collecting area, implying that their size is reduced, improve the direct-imaging performance. The predictable trend thus favors systems combining hundreds of sub-apertures of modest size, if workable designs can be evolved. One such design, the "Ubaye Hypertelescope" entering the initial testing phase in the southern Alps, has a fixed spherical meta-mirror with a 57 m effective aperture, expandable to 200 m. Preliminary results suggest that larger versions, whether spherical or active paraboloidal, can reach a kilometric aperture size at terrestrial sites having a suitable concave topography. In space, hypertelescope meta-apertures spanning up to 100 000 km are in principle feasible in the form of a flotilla of mirrors, driven by micro-thrusters or by the radiation pressure of the Sun or lasers.

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Co-phasing of a diluted aperture synthesis instrument for direct imaging: Experimental demonstration on a temporal hypertelescope

Cited by 3 publications

References 28 publications

Co-phasing of a diluted aperture synthesis instrument for direct imaging

Co-phasing of a diluted aperture synthesis instrument for direct imaging

Hypertelescopes: The Challenge of Direct Imaging at High Resolution

Hypertelescopes: The Challenge of Direct Imaging at High Resolution

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