Resolution of photothermal tomographic imaging of subsurface defects in metals with ray optic reconstruction

A capacitive photopyroelectric tomographic technique to obtain photothermal images of cross-sections with subsurface defects of opaque solid samples is reported. Unlike the two-dimensional projection images obtained by conventional photothermal detection methods, a tomographic scanning sequence has been used for cross-sectional imaging of subsurface features. Ray-like propagation of thermal waves is assumed in reconstructing the images. Resolution of these tomographic images with multiple features is investigated. Sensitivity of this reconstruction method to the size and shape of a single subsurface defect is also discussed.