Comparison of Laser Triangulation, Phase Shift Triangulation and Swept Source Optical Coherence Tomography for Nondestructive Inspection of Objects with Micrometric Accuracy

We compare the performance of laser triangulation, phase shift triangulation and swept source optical coherence tomography (SSOCT) for quantitative nondestructive inspection. Measurement accuracies of these three optical 3D imaging techniques can be reduced to a few tens of micrometers or less, making it possible to locate and geometrically characterize defects at the micrometric scale. We consider surfaces with different optical properties and we discuss the ability of these techniques to reconstruct the surface profiles. For opaque surfaces, the three techniques provide very similar results. For semi-transparent and transparent surfaces, the accuracy achieved by SSOCT relies on the capability of detecting, selecting and classifying peaks in each axial scan (A-scan), while the performance of triangulation techniques depend on several parameters including the sensitivity and the exposition time of the camera, the positioning of the system in relation to the surface, etc. Based on these facts, a prospective discussion is attempted on the possibility to combine SSOCT and phase shift triangulation for quantitative surface inspection of objects as well as for internal geometrical characterization of semi-transparent and transparent objects.