HARMONI at ELT: system analysis and performance estimation of the high-contrast module

HARMONI is the first light visible and near-IR integral field spectrograph for the ELT. It covers a large spectral range from 450nm to 2450nm with resolving powers from 3500 to 18000 and spatial sampling from 60mas to 4mas. It can operate in two Adaptive Optics modes - SCAO (including a High Contrast capability) and LTAO - or with NOAO. The project is preparing for Final Design Reviews. The high-contrast module (HCM) has been designed to characterize planets as close as 100mas from their host star (goal: 50mas), and presenting a 1e-6 flux ratio with it. To do so, it will use (1) a passive atmospheric dispersion corrector, (2) a set of amplitude apodizers and focal plane masks to lower the diffracted intensity next to the star and attenuate the PSF core, (3) a dedicated Zernike wavefront sensor to track the non-common path aberrations with the SCAO subsystem at a 0.1Hz frequency, and (4) post-processing algorithms that will rely on the temporal and spectral diversity of the IFS data to separate the planetary signals from the noise. This communication details several trade-off analyses involved in the co-design of the hardware of the HCM. It also presents contrast performance estimates that have been derived through an analysis of post-processed, simulated IFS data obtained with an end-to-end numerical model of the HCM and the rest of HARMONI. The respective interests of ADI and molecular mapping are compared in this specific case.