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 ~10-μm 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.
© 2000 Optical Society of America
Jinpin Ying, Feng Liu, P. P. Ho, and R. R. Alfano, "Nondestructive evaluation of incipient corrosion in a metal beneath paint by second-harmonic tomography," Opt. Lett. 25, 1189-1191 (2000)