Figure 3.

(a) Plot of the amplitude of $Z_2^2$ (circles) and $Z_2^{-2}$ (squares) determined by phase retrieval vs. the amplitude of $Z_2^2$ set on the deformable mirror. The solid lines are linear fits to the data. The slope of the fit to $Z_2^2$ is 0.96 and the RMSE is 20.9nm. The slope of the fit to $Z_2^{-2}$ is 0.0097 and the RMSE is 9.9nm. (b) Plot of the amplitude of $Z_1^{-1}$, $Z_1^1$, and $Z_2^0$ determined by phase retrieval vs. the amplitude of $Z_2^2$ set on the deformable mirror. There is substantial drift from measurement to measurement.