Geometry Adaptive Photothermal Coherence Tomography and Its Application in Additively Manufactured Metal Structures

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Abstract Infrared thermography has been widely applied in aerospace and other technological fields. However, constrained by perspective projection effects and the diffusive, non-wave nature of heat propagation, conventional methods are limited to generating 2D projections that reflect depth-integrated information, primarily as surface temperature. Consequently, they fail to provide intuitive inspection results for complex structures and make it difficult to quantitatively evaluate internal defects. Here, we propose a geometry adaptive photothermal coherence tomography (GA-PCT) technique to enable 3D morphology reconstruction and quantitative defect depth analysis in additively manufactured metallic components. GA-PCT performs line-structured light scanning via galvanometer-controlled laser deflection, while an infrared camera synchronously captures the thermal fringe for rapid reconstruction of surface morphology. By incorporating beam homogenization and delayed-sampling strategies into the photothermal tomography technique, accurate defect-depth analysis is achieved. Unlike existing photothermal tomography methods that form a volumetric impression by assembling depth-related 2D feature maps, GA-PCT directly outputs 3D coordinates encompassing both surface and internal features. Compared with optical 3D imaging and optical coherence tomography, which are limited to reconstructing only surface or near-subsurface features, as well as point-by-point scanning techniques such as X-ray CT and photoacoustic tomography, GA-PCT offers remarkable advantages in information completeness (with an effective penetration depth of 1.4 mm in stainless steel) and detecting efficiency (≥ 10 cm2/s), showing great potential for applications in non-destructive testing and reverse engineering.