ELT-HIRES the high resolution spectrograph for the ELT: implementing exoplanet atmosphere reflection detection with a SCAO module

The HIRES-ELT instrument foresees an observing mode that delivers integral field high resolution spectroscopy with spatial sampling down to the diffraction limit of the ELT telescope. The IFU-SCAO module presented here is sub-system of the front-end of HIRES-ELT that includes two modules: SCAO and IFU. The first is the wavefront sensor, based on a pyramid beam-splitter, that provides the guiding on the reference star and the analysis of the incoming wavefront; the second is the module that transforms the incoming f/17.7 light beam from the telescope to the appropriate f/numbers to feed the spectrometer fibers-array with the required spatial scale. In this paper, we will present the SCAO optical design to allow the exoplanet atmosphere detection in reflection. To achieve this goal, we studied a feasible pyramid wavefront sensor to be inserted in a sliding arm of the HIRES front end. The CCD camera is based on a CCD220 chip in which will be imaged the telescope pupil, sampled with a 90x90 sub-aperture grid. A total of 4089 Karhunen-Loeve modes have been generated and used to close an end-to-end simulation. The AO loop runs up to 1000 KHz and it allows to shrink the PSF to the diffraction limits of the telescope ant to achieve Strehl Ratio (SR) above 70% in best seeing case up to magnitude 15 in H-band and a SR permanently above 40%, same band, up to magnitude 14 in case of median seeing. For λ=1600nm the 50% of energy is reached before 1 λ/D for all the plotted I-magnitude under the best seeing conditions. Under Median seeing conditions, the 50% is reached before 2λ/D up to I-mag 13. For λ=1000nm instead, we reach the 50% of encircled energy before a radius of 2λ/D for I-mag less than 14 and after 5λ/D for I-mag greater than 15 in the best seeing case. For each IFU spatial sampling and resolution, we can reach a contrast of 10 3 at a distance of 4 spaxels from central peak.