Abstract:
Most ground-based adaptive optics systems use one of a small number of wavefront sensor technologies, notably (for
relatively high-order systems) the Shack-Hartmann sensor, which provides local measurements of the phase slope (first
derivative) at a number of regularly-spaced points across the telescope pupil. The curvature sensor, with response
proportional to the second derivative of the phase, is also sometimes used, but has undesirable noise propagation
properties during wavefront reconstruction as the number of actuators becomes large. It is interesting to consider the use
for astronomical adaptive optics of the "phase contrast" technique, originally developed for microscopy by Zemike to
allow convenient viewing of phase objects. In this technique, the wavefront sensor provides a direct measurement of the
local value of phase in each subaperture of the pupil. This approach has some obvious disadvantages compared to Shack-Hartmann wavefront sensing, but has some less obvious but substantial advantages as well. Here we evaluate the relative merits in a practical ground-based adaptive optics system.
