Three-dimensional optical profilometry for artwork inspection

A special fibre-optic interferometer is proposed for 3D profilometry. Sinusoidal 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 captured by a CCD camera. Subsequently, the captured image is analysed, and the relationship between the fringe phase and the height distribution of the illuminated surface is derived. The proposed method is simple and accurate. It is suitable for automatic measurements. Detailed theoretical and experimental results are presented. Tests show that the system can detect indents and outdents with a maximum depth of less than 10 mu m.