COATING TECHNIQUES IN OPTICAL INTERFEROMETRIC METROLOGY

In optical interferometry diffuse reflectivity of the surface under st udy should be high and homogeneous. Application of a white reflective coating can strongly improve measurement results. The optical properti es of bronze powder, TiO2 powder, white Chinese ink, and MgO coatings are discussed. Measurements of reflected intensity distribution show t hat white Chinese ink and MgO have superior optical characteristics, a nd electron microscopy shows that these coatings cause thickness artif acts of less than 7.5 and 17 mu m, respectively. The effect on deforma tion measurements is demonstrated by moire topography on a thin membra ne that is deformed under small static pressures. The membrane center displacement varies from 15 to 100 mu m, and within a measuring precis ion of 2.5 mu m no artifacts on this deformation are found. (C) 1997 O ptical Society of America.