Shack-Hartmann and Interferometric Hybrid Wavefront Sensor

Wavefront sensors (WFS) use intensity measurements to estimate the phase of an incident optical field for applications such as high-quality surface measurements and atmospheric compensation with adaptive optics (AO). Shack-Hartmann (SH) WFS’s use intensity measurements at the focal plane to estimate local wavefront tilts, which can be reconstructed into wavefront estimates. Self-referencing-interferometer (SRI) WFS’s use pupil-plane interferogram-intensity measurements to estimate the phase of the incident optical field. The SRI and SH WFS’s have strengths and weaknesses that turn out to complement each other quite well over a range of operating conditions. Specifically, the difference between the mathematical formulation of SRI measurements and the actual phase at DM actuators has been shown to be insensitive to scintillation. In contrast, the SH WFS’s formulation error can be significant in strong scintillation. Conversely, the SH WFS has actually shown better performance than the SRI in cases of low scintillation strength and large subapertures relative to atmospheric coherence width. Together, the SRI and the SH WFS provide better performance over a wider range of atmospheric conditions than either WFS could do on its own. This document reports results of wave-optics simulations used to test the performance of a hybrid WFS designed to combine the SRI and SHWFS’s in an optimal way. Optimal hybrid-WFS design required a thorough analysis of the noise characteristics of each WFS to produce noise models that assist in the design of an optimal phaseestimation algorithm. Feasible architectures and algorithms for combining WFS’s were chosen, and the noise models of the individual WFS’s were combined to form a model for the noise-induced error of the resulting hybrid WFS. The hybrid WFS and phase-estimation algorithm developed through this work showed improvement over a comparable stand-alone SRI in open-loop wave-optics simulations.