Three-dimensional optical profilometry for artwork inspection

A special fibre-optic interferometer is proposed for 3D profilometry. Sinus oidal fringes are produced by the interference of two spherical wavefronts emitted from the output fibres of a directional coupler. The fringe pattern is projected on an object surface and the deformed grating image is captur ed by a CCD camera. Subsequently, the captured image is analysed, and the r elationship between the fringe phase and the height distribution of the ill uminated surface is derived. The proposed method is simple and accurate. It is suitable for automatic measurements. Detailed theoretical and experimen tal results are presented. Tests show that the system can detect indents an d outdents with a maximum depth of less than 10 mu m.