Deflectometry for measuring mount-induced mirror surface deformations

Deflectometry has been proven as a high precision and high dynamic range surface metrology technique. We report on the use of deflectometry to diagnose mount-induced optical surface deformations. A surrogate mirror from the OLI-2 earthobserving satellite mission is tested with deflectometry in a non-null configuration using only a CCD camera and an LCD computer monitor. Moments are mechanically induced at each flight-like mirror mount and the deformed surface is measured. Systematic errors in the surface measurements are significantly reduced by maintaining a consistent measurement geometry and evaluating moment-induced deformations differentially. The surface deformation modes from orthogonal moments at each mirror mount are compared to FEA predictions. The agility of this metrology sets the groundwork for in situ measurements of flight aspheric mirror surface deformations during component integration and prior to system testing.