  We discuss the use of parametric phase-diverse phase retrieval as an in-situ
high-fidelity wavefront measurement method to characterize and optimize the
transmitted wavefront of a high-contrast coronagraphic instrument. We apply our
method to correct the transmitted wavefront of the HiCAT (High contrast imager
for Complex Aperture Telescopes) coronagraphic testbed. This correction
requires a series of calibration steps, which we describe. The correction
improves the system wavefront from 16 nm RMS to 3.0 nm RMS.
