Coating techniques in optical interferometric metrology

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