Improving VLT/SPHERE without additional hardware: comparing quasi-static correction strategies

Direct imaging is the primary technique currently used to detect young and warm exoplanets and understand their formation scenarios. The extreme flux r atio b etween a n e xoplanet a nd i ts h ost s tar r equires t he u se of coronagraphs to attenuate the starlight and create high contrast images. However, their performance is limited by wavefront aberrations that cause stellar photons to leak through the coronagraph and on to the science detector preventing the observation of fainter extrasolar companions. The VLT/SPHERE instrument takes advantage of its efficient ad aptive op tics sy stem to mi nimize dy namical ab errations to im prove th e im age co ntrast. In good seeing conditions, the performance is limited by quasi-static aberrations caused by slowly varying aberrations and manufacturing defects in the optical components. The mitigation of these aberrations requires additional wavefront sensing and control algorithms to enhance the contrast performance of SPHERE. Dark hole algorithms initially developed for space-based application and recently performed on SPHERE calibration unit have shown significant i mprovement i n c ontrast. T his w ork p resents a s tatus u pdate o f d ark h ole a lgorithms a pplied on SPHERE and the results obtained during the on-sky tests performed on February 15th 2022.