Nondestructive evaluation of incipient corrosion in a metal beneath paint by second-harmonic tomography

A second-harmonic optical scanning imaging method for nondestructive evalua tion of corrosion of painted metals is demonstrated. Two-dimensional images of the sectional structure from a sample of painted metal with corrosion w ere obtained by detection of second-harmonic generation (SHG). The second-h armonic signals generated from paint, corrosion, and metal can be spatially imaged in similar to 10-mu m sliced subsurface layers. Corroded metal laye rs covered with paint are found to have more intensity variation than norma l 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. (C) 2000 Optical Society of America. OCIS codes: 190.0190, 110.6960, 180.5810.