Three years of harvest with the vector vortex coronagraph in the thermal   infrared
  For several years, we have been developing vortex phase masks based on sub-wavelength gratings, known as Annular Groove Phase Masks. Etched onto diamond substrates, these AGPMs are currently designed to be used in the thermal infrared (ranging from 3 to 13 {\mu}m). Our AGPMs were first installed on VLT/NACO and VLT/VISIR in 2012, followed by LBT/LMIRCam in 2013 and Keck/NIRC2 in 2015. In this paper, we review the development, commissioning, on-sky performance, and early scientific results of these new coronagraphic modes and report on the lessons learned. We conclude with perspectives for future developments and applications. 
Olivier Absil, Dimitri Mawet, Mikael Karlsson, Brunella Carlomagno,   Valentin Christiaens, Denis Defr\`ere, Christian Delac...
astro-ph.IM