Method and apparatus for absolutely measuring flat and sperical surfaces with high spatal resolution

A system for absolute surface testing of planar or spherical surfaces including in combination:

• a phase shifting interferometer having a reference surface position and a test surface position for holding, respectively, a reference element and a test element in alignment with one another, with the reference surface position being fixed with respect to the remainder of elements of the interferometer and the test surface position mounted on a test piece mount including mechanisms for:
• (A) effecting tilt of the test element in the y axis,
• (B) effecting tipping of the test element in the x axis,
• (C) angularly rotating the test element relative to the reference surface, and
• (D) effecting orthogonal translation of the test element in both the x and y directions;
• means for producing measured difference maps of first (A), second (B), and third (C) test elements in the following combinations at the reference surface positions and the test surface positions:
• Measurement m1:reference surface=A, test surface=C
• Measurement m2:reference surface=B, test surface=C
• Measurement m3:reference surface=B, test surface=A and at least two more rotational positions of flat A at the test surface position:
• Measurement m4:reference surface=B, test surface=A rotated by α1,
• Measurement m5:reference surface=B, test surface=A rotated by means for calculating rotationally sheared surface maps of the first test element A:
• and
• means for utilizing the measured difference maps and the rotationally sheared surface maps to produce absolute surface maps of the first (A), second (B), and third (C) test pieces.