A second-harmonic optical scanning imaging method for nondestructive evaluation of corrosion of painted metals is demonstrated. Two-dimensional images of the sectional structure from a sample of painted metal with corrosion were obtained by detection of second-harmonic generation (SHG). The second-harmonic signals generated from paint, corrosion, and metal can be spatially imaged in sliced subsurface layers. Corroded metal layers covered with paint are found to have more intensity variation than normal polished metal. The spatial mapping of the second-harmonic signals shows depth differentiation of paint, corrosion, and metal surfaces. The depth of corrosion beneath the paint can be measured from the SHG images.
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