TPF-C Technology Plan - Exoplanet Exploration Program - NASA

Chapter 3
The wavefront quality of the occulting mask substrate must also be considered. Mask errors
drive the requirement for spot centration. Mask substrate errors also impact the static error
budget because the errors can be compensated by the DM for only a single spectral wavelength.
Approach
The small optics are reflective and coated with protected silver. The contribution of the coating
to the surface quality must be considered. The incident angle on most of these optics is near
normal incidence, thereby minimizing coating effects. Two folding flats are at 45 degrees, but
will pair-wise cancel each other’s polarization effects. To meet the beamwalk requirements, the
surface flatness of these optics must be