Fundamental gain in high contrast imaging with the

F. Patru, S. Esposito, A. Puglisi, A. Riccardi, E. Pinna, C. Arcidiacono, J. Hill, P. Hinz

Research output: Contribution to journalConference articlepeer-review


Numerical simulations for the LBTI have shown a fundamental gain in contrast when using two 8m adaptive optics telescopes instead of one. The LBTI provides an "in-between" PSF, combining both diffractive and interferometric properties (Fig. 1). The maximum intensity in the PSF is increased by a factor of four, accounting for the double flux and the fringe intensification. The imaging performance of the LBTI is limited by the AO-correction level, as for a single LBT aperture (Fig. 3,4). The PSFs are computed by using 2 time series of residual wavefronts with an RMS of ~ 100nm yielding an AO Strehl of 50% in R band (visible). The contrast gain map is defined as the normalised ratio of the PSF of a single LBT over the PSF of the LBTI. The contrast gain averaged across the field is improved by a factor 2 in contrast by using the long exposures and by a factor of 10 in contrast by using the short exposures (Fig. 5,6). Indeed, contrary to the long exposure where the fringes are blurred, a snapshot retains the fringes formed in a halo of speckles (Fig. 3), enabling speckle imaging. The speckle halo contains not only high angular resolution information but also high contrast imaging information. Thus, there is some gain in grouping some short exposures with high gain. A gain zone is produced in the valleys of the PSF formed by the dark Airy rings and/or the dark fringes. A huge contrast gain (G ~ 100 to 1000) in narrow zones (few mas) can be achieved when both a dark fringe and a dark ring overlap. The Earth rotation allows to exploit various area in the contrast gain map in which a planet passes through several gain zones. This makes the LBTI well suitable for the Angular Differential Imaging (ADI) technique. A rotation of 15°. is sufficient to pass through at least one contrast gain zone (Fig. 7). A planet is located in a white or in a dark ring, depending on its radial distance. A planet is alternatively located in a white fringe (G ~ 1) or in a dark fringe (G ~ 10 to 100) as a function of the parallactic angle (Fig. 8,9).

Original languageEnglish (US)
Article number1001505
JournalProceedings of SPIE - The International Society for Optical Engineering
StatePublished - Jul 29 2018
Externally publishedYes
EventSPIE Astronomical Telescopes and Instrumentation 2016 - Edinburgh, United Kingdom
Duration: Jun 26 2016Jul 1 2016

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Condensed Matter Physics
  • Computer Science Applications
  • Applied Mathematics
  • Electrical and Electronic Engineering


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