High-Contrast Mode
High Contrast mode in HARMONI is a specialised operating configuration of the Single Conjugate Adaptive Optics system that is optimised to suppress residual starlight close to a bright on-axis target, enabling the detection and spectroscopy of faint companions such as exoplanets.
In HCM the exoplanet-imaging capability depends on an apodized pupil coronagraph placed in the optical path to suppress diffraction from the host star and improve achievable contrast. The apodizer modifies the amplitude transmission across the telescope pupil in a smooth way so that downstream, after focal-plane masks or stops, the light from the bright star is redistributed into regions where it can be blocked or strongly reduced, enhancing contrast for faint companions. This apodized pupil coronagraph is an integral part of the HCM design to reach contrasts on the order of 10⁻⁶ at small angular separations
