Optical aperture synthesis with electronically connected telescopes

Dravins, Dainis; Lagadec, Tiphaine; Nuñez, Paul D.

doi:10.1038/ncomms7852

Cited by 38 publications

(22 citation statements)

References 15 publications

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“…At bottom left is an actually measured second-order optical coherence pattern (in false colors) from an artificial asymmetric binary star, built up from intensity-correlation measurements over 180 baselines between pairs of small laboratory telescopes. At right is the image reconstructed from these intensity-interferometric measurements [54][55] . The circle marks the diffraction-limited spatial resolution, thus realized by an array of optical telescopes connected through electronic software only, with no optical links between them.…”

Section: Aperture-synthesis Imaging With Large Optical Arraysmentioning

confidence: 99%

“…Also that ambiguity, however, might be resolved by supplementing the data with, e.g., lower-resolution measurements from single telescopes, and enforcing image continuity. Figure 2 shows an example of actual measurements of an artificial star with an array of small optical telescopes in the laboratory, operated as an intensity interferometer with 180 baselines [54][55] .…”

Section: Aperture-synthesis Imaging With Large Optical Arraysmentioning

confidence: 99%

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Intensity interferometry: optical imaging with kilometer baselines

Dravins

2016

SPIE Proceedings

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Optical imaging with microarcsecond resolution will reveal details across and outside stellar surfaces but requires kilometer-scale interferometers, challenging to realize either on the ground or in space. Intensity interferometry, electronically connecting independent telescopes, has a noise budget that relates to the electronic time resolution, circumventing issues of atmospheric turbulence. Extents up to a few km are becoming realistic with arrays of optical air Cherenkov telescopes (primarily erected for gamma-ray studies), enabling an optical equivalent of radio interferometer arrays. Pioneered by Hanbury Brown and Twiss, digital versions of the technique have now been demonstrated, reconstructing diffraction-limited images from laboratory measurements over hundreds of optical baselines. This review outlines the method from its beginnings, describes current experiments, and sketches prospects for future observations.

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Section: Aperture-synthesis Imaging With Large Optical Arraysmentioning

confidence: 99%

Section: Aperture-synthesis Imaging With Large Optical Arraysmentioning

confidence: 99%

Intensity interferometry: optical imaging with kilometer baselines

Dravins

2016

SPIE Proceedings

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“…This principle has been used in many fields, such as for synthetic aperture radar (SAR) [1], [2], [3], synthetic aperture radio telescopes (SART) [4], [5], interferometric synthetic aperture microscopy (ISAM) [6], synthetic aperture sonar (SAS) [7], [8], synthetic aperture ultrasound (SAU) [9], [10], and synthetic aperture LiDAR (SAL) / synthetic aperture imaging laser (SAIL) [11], [12].…”

Section: Introductionmentioning

confidence: 99%

A Statistical View on Synthetic Aperture Imaging for Occlusion Removal

2019

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Synthetic apertures find applications in many fields, such as radar, radio telescopes, microscopy, sonar, ultrasound, LiDAR, and optical imaging. They approximate the signal of a single hypothetical wide aperture sensor with either an array of static small aperture sensors or a single moving small aperture sensor. Common sense in synthetic aperture sampling is that a dense sampling pattern within a wide aperture is required to reconstruct a clear signal. In this article we show that there exists practical limits to both, synthetic aperture size and number of samples for the application of occlusion removal. This leads to an understanding on how to design synthetic aperture sampling patterns and sensors in a most optimal and practically efficient way. We apply our findings to airborne optical sectioning which uses camera drones and synthetic aperture imaging to computationally remove occluding vegetation or trees for inspecting ground surfaces.

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“…For reconstructing the image of the single elliptical star from the coherence patterns in Figure 6 (bottom), the compactness regularization was used with µ = 10 11 , for the symmetric binary (Figure 6, top) the smoothness regularization was applied with µ = 10 14 , and for the asymmetric one (Figure 7) µ = 10 13 . The resulting reconstructed images are in Figure 8, for which a shorter description appeared in Dravins et al (2015).…”

Section: Image Reconstructionmentioning

confidence: 99%

Long-baseline optical intensity interferometry

Dravins

Lagadec

Nuñez

2015

A&A

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Context. A long-held vision has been to realize diffraction-limited optical aperture synthesis over kilometer baselines. This will enable imaging of stellar surfaces and their environments, and reveal interacting gas flows in binary systems. An opportunity is now opening up with the large telescope arrays primarily erected for measuring Cherenkov light in air induced by gamma rays. With suitable software, such telescopes could be electronically connected and also used for intensity interferometry. Second-order spatial coherence of light is obtained by cross correlating intensity fluctuations measured in different pairs of telescopes. With no optical links between them, the error budget is set by the electronic time resolution of a few nanoseconds. Corresponding light-travel distances are approximately one meter, making the method practically immune to atmospheric turbulence or optical imperfections, permitting both very long baselines and observing at short optical wavelengths. Aims. Previous theoretical modeling has shown that full images should be possible to retrieve from observations with such telescope arrays. This project aims at verifying diffraction-limited imaging experimentally with groups of detached and independent optical telescopes. Methods. In a large optics laboratory, artificial stars (single and double, round and elliptic) were observed by an array of small telescopes. Using high-speed photon-counting solid-state detectors and real-time electronics, intensity fluctuations were cross-correlated over up to 180 baselines between pairs of telescopes, producing coherence maps across the interferometric Fourier-transform plane. Results. These interferometric measurements were used to extract parameters about the simulated stars, and to reconstruct their twodimensional images. As far as we are aware, these are the first diffraction-limited images obtained from an optical array only linked by electronic software, with no optical connections between the telescopes. Conclusions. These experiments serve to verify the concepts for long-baseline aperture synthesis in the optical (somewhat analogous to radio interferometry) and to optimize the instrumentation and observing procedures for future observations with large arrays of Cherenkov telescopes, aiming at order-of-magnitude improvements of the angular resolution in optical astronomy.

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Optical aperture synthesis with electronically connected telescopes

Cited by 38 publications

References 15 publications

Intensity interferometry: optical imaging with kilometer baselines

Intensity interferometry: optical imaging with kilometer baselines

A Statistical View on Synthetic Aperture Imaging for Occlusion Removal

Long-baseline optical intensity interferometry

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