US Patent 10267618 Defect detection method and defect detection apparatus

A defect detection apparatus is provided that can inspect a measurement region of a target object at one time and without inconsistencies arising within the measurement region. A defect detection apparatus 10 includes: a generation unit (signal generator 11 and vibrator 12) for generating an elastic wave in a target object S; an illumination unit (pulsed laser light source 13 and illumination light lens 14) for performing stroboscopic illumination onto a measurement region of a surface of the target object S; and a displacement measurement unit (speckle shearing interferometer 15) for collectively measuring displacements in a normal direction at each point of the measurement region with respect to at least three mutually-different phases of the elastic wave by controlling a phase of the elastic wave and a timing of the stroboscopic illumination. Defects in the measurement region are detected based on the displacements in the normal direction at each point of the measurement region with respect to at least three phases that are obtained by the displacement measurement unit.