High - Speed High - Resolution Subsurface Defect Detection in Ceramics Using Optical Gating Techniques

Optical gating techniques and in particular optical coherence tomography (OCT) have recently been used as a noninvasive probe in the medical field[1 ,2] and as a nondestructive probe in material analysis[3-5]. Indeed, any medium which has some light penetration below the surface can potentially be analyzed with OCT. The depth at which a signal can be detected depends both on light absorption and scattering, with the second playing a more critical role in most materials of interest. In this work we concentrate on the application of OCT towards defect detection in ceramic materials. For the various ceramics that we have analyzed in the laboratory, the maximum penetration depths ranged from a few tens of microns to approximately one millimeter below the surface. Because of this limited penetration depth, OCT can not be applied to detect defects buried deep below the surface in ceramic materials. However, because operational stresses of many ceramic components are greatest in the near-surface region, the defects at or just below the surface are the most important to detect.