Authors

Mala Mateen, Olivier Guyon, Michael Hart.

Affiliations

University of Arizona, University of Arizoan, University of Arizona.

Abstract

In this paper we present results from a side‐by‐side comparison of the non‐linear curvature wavefront sensor (nlCWFS) with the Shack‐ Hartmann wavefront sensor (SHWFS). The non‐linear curvature technique is derived from the successful curvature wavefront sensing concept, but uses a non‐linear wavefront reconstruction scheme. The nlCWFS approaches the theoretical sensitivity limit imposed by fundamental physics by taking 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 (λ/D) rather than the seeing limit of more conventional linear WFSs. The large ratio between the diffraction limit of an Extremely Large Telescope (ELT) and the seeing limit makes the nlCWFS significantly more sensitive than conventional wavefront sensors. The nlCWFS offers high sensitivity on reasonably bright targets mV < 15.

In our last paper we showed verification of the nlCWFS technique and an initial comparison of the nlCWFS with the SHWFS at monochromatic light. In this paper we extend the analysis to polychromatic light. We have designed an experiment that allows for polychromatic compensation by use of refractive optics and minimizes chromatic aberration of the diffraction‐limited speckles. The current design is ready to be implemented on a telescope. We show results from a comparison of the wavefront correction preformed by the nlCWFs and the SHWFS for broadband imaging. Phase Wheels are used to generate atmospheric turbulence in the lab. Our results show that the exquisite control of low order aberrations by the nlCWFS delivers significant gain in sensitivity over the SHWFS.