Geometry adaptive photothermal coherence tomography and its application in additively manufactured metal structures

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 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 detection efficiency (≥10 cm²·s⁻¹), showing great potential for applications in non-destructive testing and reverse engineering.