ERIS
The Enhanced Resolution Imager and Spectrograph (ERIS) is an imager for J-M band and integral-field spectrograph for J-K band to be installed in the Cassegrain focus of UT4 at the Very Large Telescope. The goal of ERIS is to provide diffraction limited imaging and integral-field spectroscopy in the 1 to 5 micron wavelength range. To this end, ERIS has an AO system consisting of the deformable secondary mirror of UT4 and a Shack-Hartmann wavefront sensor.
One of the coronagraphs deployed in the imaging arm of ERIS is the vAPP. The vAPP is designed to provide one-sided dark holes over the 2 to 5 micron wavelength range. The dark hole is designed to have a contrast of 10^-5 between 2 and 15 lambda/D. The pupil for which the vAPP is designed has an asymmetric feature, because the (warm) tertiary mirror has to be moved aside to send light to ERIS. This pupil amplitude asymmetry enables focal-plane wavefront sensing with the ERIS vAPP by either using the in Leiden developed non-linear wavefront sensing algorithm or spatial linear dark field control. Furthermore, the design includes two additional holograms that can be used as astrometric and photometric references for exoplanet characterization.
