Multi-Conjugate AO
The Multi-Conjugate Adaptive Optics (MCAO) mode of HARMONI is designed to deliver high and uniform image quality over a significantly larger Sky Coverage than Single Conjugate Adaptive Optics, while maintaining near-diffraction-limited performance in the near-infrared. MCAO achieves this by correcting atmospheric turbulence in three dimensions rather than along a single line of sight.
In MCAO mode, wavefront distortions are measured using multiple guide stars distributed across the field, combining natural guide stars with laser guide stars provided by the ELT adaptive optics facility MORFEO. These measurements are used to reconstruct the vertical structure of atmospheric turbulence through tomographic algorithms. The reconstructed turbulence profile is then corrected using multiple deformable mirrors conjugated to different altitudes in the atmosphere, allowing the system to compensate both ground-layer and higher-altitude aberrations. This approach significantly reduces anisoplanatism and produces a more uniform point spread function across the science field.
Simulations and system budgets indicate near-infrared Strehl ratios of order 30–50% in K band under median conditions, with a stable and spatially homogeneous point spread function across fields of several tens of arcseconds. The delivered image quality is well matched to intermediate spaxel scales and to science cases requiring uniform resolution and sensitivity across extended targets.