A new wavefront sensing approach , derived from the successful curvature wavefront sensing concept but using a non-linear phase retrieval wavefront reconstruction scheme , is described .
The non-linear curvature wavefront sensor ( nlCWFS ) approaches the theoretical sensitivity limit imposed by fundamental physics by taking full advantage of wavefront spatial coherence in the pupil plane .
Interference speckles formed by natural starlight encode wavefront aberrations with the sensitivity set by the telescope ’ s diffraction limit \lambda /D rather than the seeing limit of more conventional linear WFSs .
Closed-loop adaptive optics simulations show that with a nlCWFS , a 100 nm RMS wavefront error can be reached on a 8-m telescope on a m _ { V } = 13 natural guide star .
The nlCWFS technique is best suited for high precision adaptive optics on bright natural guide stars .
It is therefore an attractive technique to consider for direct imaging of exoplanets and disks around nearby stars , where achieved performance is set by wavefront control accuracy , and exquisite control of low order aberrations is essential for high contrast coronagraphic imaging .
Performance gains derived from simulations are shown , and approaches for high speed reconstruction algorithms are briefly discussed .