Development of the non-linear curvature wavefront sensor

The non-linear Curvature Wavefront Sensor (nlCWFS) is derived from the successful curvature wavefront sensing principle but uses a non-linear reconstruction algorithm to maintain sensitivity to low order modes. It can deliver diffraction-limited images in the visible. Use of the full spatial coherence of the pupil allows the nlCWFS (D/r0)2 gain in sensitivity, over the SHWFS, at the lowest spatial frequency. When background limited the nlCWFS sensitivity scales as D4, a combination of D2 gain due to the diffraction limit and D2 gain due to the telescope's collecting power. For a 30m telescope (TMT) with a seeing of 0.5, the nlCWFS requires 22, 500 fewer photons than the SHWFS to deliver the same wavefront measurement accuracy at the lowest spatial frequencies.