Single conjugate adaptive optics for the ELT instrument METIS

Abstract

The European Extremely Large Telescope (ELT) is a 39 m large, ground-based optical and near-to mid-infrared telescope under construction in the Chilean Atacama desert. Operation is planned to start around the middle of the next decade. All first light instruments will come with wavefront sensing devices that allow control of the ELT's intrinsic M4 and M5 wavefront correction units, thus building an adaptive optics (AO) system. To take advantage of the ELT's optical performance, full diffraction-limited operation is required and only a high performance AO system can deliver this. Further technically challenging requirements for the AO come from the exoplanet research field, where the task to resolve the very small angular separations between host star and planet, has also to take into account the high-contrast ratio between the two objects. We present in detail the results of our simulations and their impact on high-contrast imaging in order to find the optimal wavefront sensing device for the METIS instrument. METIS is the mid-infrared imager and spectrograph for the ELT with specialised high-contrast, coronagraphic imaging capabilities, whose performance strongly depends on the AO residual wavefront errors. We examined the sky and target sample coverage of a generic wavefront sensor in two spectral regimes, visible and near-infrared, to pre-select the spectral range for the more detailed wavefront sensor type analysis. We find that the near-infrared regime is the most suitable for METIS. We then analysed the performance of Shack-Hartmann and pyramid wavefront sensors under realistic conditions at the ELT, did a balancing with our scientific requirements, and concluded that a pyramid wavefront sensor is the best choice for METIS. For this choice we additionally examined the impact of noncommon path aberrations, of vibrations, and the long-term stability of the SCAO system including high-contrast imaging performance.Keywords Single conjugate adaptive optics · SCAO · ELT · Pyramid wavefront sensor · Shack-Hartmann wavefront sensor · Fragmented pupil · Low wind effect · Non-common path aberrations · High-contrast imaging

A new method for target selection in direct imaging programmes with COPAINS

“…The sensitivity limits in terms of contrast for the future E-ELT/METIS instrument were obtained through end-to-end simulations of a 1-hour observation in the L band for a star of magnitude L = 6, using the classical vortex coronagraph and assuming an ADI sequence with 40 deg parallac-tic angle rotation (B. Carlomagno et al, in prep.). These sensitivity limits take into account residual wavefront errors from the adaptive optics system (Hippler et al 2019), as well as shot noise from the star and thermal background.…”

Advanced wavefront reconstruction methods for segmented Extremely Large Telescope pupils using pyramid sensors

“…For instance, the influence of wind shake and NCPAs on the METIS performance has been previously analyzed in Ref. 40. In this paper, we focus on eliminating the impact of spiders in the first turn.…”

Real-time adaptive optics with pyramid wavefront sensors: part II. Accurate wavefront reconstruction using iterative methods

“…For comparison, the pyramid sensor with modulation 4 λ/D was reported to provide in the same environment the LE Strehl ratio of 0.80. As recently reported in [32], another variant of MVM, the zonal minimum variance reconstructor in the YAO simulation tool [64], which is a zonal regularized approach, achieves LE Strehl of 0.89 in case of the modulated pyramid sensor (with modulation 4) and high photon flux.…”