Absolute interferometric testing of spherical surfaces

In typical interferometric testing the part under test is measured against a reference standard. The measured result is the difference between the errors in the test and reference surfaces plus any addition errors introduced by the interferometer. For accurate qualification of the reference surface it is necessary to employ a technique that can measure the part absolutely. This paper examines an existing technique for absolute testing of spherical surfaces which produces a map of the entire surface. The capabilities of this technique, error sources, and experimental data will be examined.