Holographic Imaging of Crowded Fields: High Angular Resolution Imaging with Excellent Quality at Very Low Cost

We present a method for speckle holography that is optimised for crowded fields. Its two key features are an iterativ improvement of the instantaneous Point Spread Functions (PSFs) extracted from each speckle frame and the (optional) simultaneous use of multiple reference stars. In this way, high signal-to-noise and accuracy can be achieved on the PSF for each short exposure, which results in sensitive, high-Strehl re- constructed images. We have tested our method with different instruments, on a range of targets, and from the N- to the I-band. In terms of PSF cosmetics, stability and Strehl ratio, holographic imaging can be equal, and even superior, to the capabilities of currently available Adaptive Optics (AO) systems, particularly at short near-infrared to optical wavelengths. It outperforms lucky imaging because it makes use of the entire PSF and reduces the need for frame selection, thus leading to higher Strehl and improved sensitivity. Image reconstruction a posteriori, the possibility to use multiple reference stars and the fact that these reference stars can be rather faint means that holographic imaging offers a simple way to image large, dense stellar fields near the diffraction limit of large telescopes, similar to, but much less technologically demanding than, the capabilities of a multi-conjugate adaptive optics system. The method can be used with a large range of already existing imaging instruments and can also be combined with AO imaging when the corrected PSF is unstable.Comment: Accepted for publication in MNRAS on 15 Nov 201

Validazione di Piani di Disaster Recovery mediante Simulatore

Contribution published online at: http://www.mimos.it/nuovo/contenuto_view.asp?check=10

PISTIL, moyen de métrologie pour l'évaluation des lasers à combinaison cohérente

International audiencePISTIL is an interferometric metrology tool dedicated to the analysis of regular segmented wavefront surfaces. Its ease of use and the quality of its measurements make it an ideal and independent analyzer for the diagnosis of the phasing of coherent combined lasers. The results presented here were obtained on the XCAN laser, a digital laser composed of 61 CBC laser fibers.PISTIL est un moyen de métrologie interférométrique dédié à l'analyse des surfaces d'onde segmentées régulières. Sa facilité de mise en oeuvre et la qualité de ses mesures en font un analyseur idéal et indépendant pour le diagnostic de la mise en phase des lasers à combinaison cohérente. Les résultats présentés ici ont été obtenus sur le laser XCAN, laser digital composé de 61 fibres laser CBC

Ensuring long-term stability of infrared camera absolute calibration

International audienceAbsolute calibration of cryogenic 3-5 μm and 8-10 μm infrared cameras is notoriously instable and thus has to be repeated before actual measurements. Moreover, the signal to noise ratio of the imagery is lowered, decreasing its quality. These performances degradations strongly lessen the suitability of Infrared Imaging. These defaults are often blamed on detectors reaching a different “response state” after each return to cryogenic conditions, while accounting for the detrimental effects of imperfect stray light management. We show here that detectors are not to be blamed and that the culprit can also dwell in proximity electronics. We identify an unexpected source of instability in the initial voltage of the integrating capacity of detectors. Then we show that this parameter can be easily measured and taken into account. This way we demonstrate that a one month old calibration of a 3-5 μm camera has retained its validity