VORTEX

From 2013 to 2018, PSILab has focused its research on the development of annular groove phase masks (AGPM – an implementation of vector vortex phase masks for coronagraphic applications) in collaboration with Uppsala University (ERC Starting Grant VORTEX + ULiège-based ARC grant).

T

he VORTEX project has allowed us to install vortex phase masks onto some of the world-leading infrared coronagraphic cameras, such as VLT/VISIR, VLT/NACO, Keck/NIRC2, or LBT/LMIRCam. These instruments have led to various discoveries in the field of extrasolar planetary systems, focusing mostly on the search and characterization of extrasolar planets (e.g., Absil et al. 2013, Reggiani et al. 2014, Milli et al. 2016, Ruane et al. 2017, Reggiani et al. 2018, Mawet et al. 2019) and of circumstellar disks (Milli et al. 2014, Mawet et al. 2017, Guidi et al. 2018).

Besides these discoveries, several advances have been made within the VORTEX project:

• We have developed a new pointing control algorithm, referred to as QACITS, which allows the star to be centered on the vortex phase mask with a typical precision of a few hundredths of a resolution element (~0.01 λ/D, Huby et al. 2015). This pointing algorithm has now been demonstrated on sky, and is routinely used at Keck (Huby et al. 2017) and for the VISIR/NEAR project at VLT. 
• We have improved upon state-of-the-art data reduction and analysis procedures, and proposed new high-contrast imaging algorithms based on robust low-rank approximation (LLSG, Gomez Gonzalez et al. 2016) and on supervised deep learning techniques (Gomez Gonzalez et al. 2018). We have also developed an open-source image processing package that is now used by several teams around the world (VIP, Gomez Gonzalez et al. 2017).
• The AGPM manufacturing process has been largely improved (Vargas Catalan et al. 2016a), allowing us to produce L-, M-, and N-band AGPMs reaching excellent performance levels, with peak rejection ratios beyond 1000:1 (Vargas Catalan et al. 2016b). By decreasing the period of the sub-wavelength gratings, we have pushed the operating wavelength of our AGPMs down to the K band (2 - 2.4 μm), with a demonstrated peak rejection above 200:1 (Vargas Catalan et al. 2018). Finally, we have designed and performed first manufacturing tests of vortex phase masks with topological charge 4 (Delacroix et al. 2014, Vargas Catalan et al. 2018), which are expected to provide even deeper starlight cancellation.
• We have developed and integrated a dedicated optical test bench for near-infrared coronagraphic applications, called VODCA (Jolivet et al. 2014). This test bench has allowed us to (re)assess the performance of K-, L- and M-band AGPMs (Jolivet et al. 2019), and to test new wavefront control solutions (Orban de Xivry et al. 2017).