Reflective coatings in optical interferometry for in vitro studies of the eardrum

Holography and moire topography are very valuable tools for the study of the shape, the deformation, and the vibration of delicate biological structures such as the eardrum. Best results are obtained if the object surface has high diffuse reflectivity, without specular reflections. May biological objects do not have these qualities by nature, so that application of reflective coatings can strongly improve measuring results. In the present paper the optical and mechanical properties of reflective coatings based on bronze powder, white Chinese ink, and magnesium oxide are discussed. Measurements of reflected intensity distribution show that white Chinese ink and MgO have superior optical qualities: they can strongly enhance diffuse reflectivity, while completely suppressing all specular reflections. Electron microscopy shows that these coatings have a layer thickness of 7.5 micrometer and 17 micrometer, respectively. Phase shift moire topography is used to measure the displacement of a thin plastic membrane which is deformed by small static pressures. It is shown that the coatings do not cause deformation artifacts within the measuring resolution of 2.5 micrometers. Application results of in-vitro shape and deformation measurements on coated tympanic membranes are given.© (1996) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.