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8 September 1995 Automatic inspection of defects on optical surfaces by recognition of forescattering patterns
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An optoelectronic device for automatically inspecting optical surface defects by recognition of forescattering patterns is described. A light spot coming from a diode laser scans the optical surface following a track of spiral. The normal light falls into an optical trap. The forescattered light by the surface defect is projected on a CCD array where the forescattering patterns are formed. Different kinds of defects make very different patterns. By recognition of the patterns using a computer, the shape and size of a defect are obtained simultaneously. The device can inspect the defects both on the surface and under the surface efficiently. The light spot takes the shape of a sharp line in order to improve the detectability of the scratches. Through a rotating Dove prism, this sharp line spins while spirally scanning the surface so as to meet the surface scratches. The effect of dust on the surface under examiniation is minimized. The experimental results show that this device can detect the scratches which are only just visible to a trained inspector.
© (1995) COPYRIGHT Society of Photo-Optical Instrumentation Engineers (SPIE). Downloading of the abstract is permitted for personal use only.
Yongjun Wu "Automatic inspection of defects on optical surfaces by recognition of forescattering patterns", Proc. SPIE 2536, Optical Manufacturing and Testing, (8 September 1995);

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