Laser-projected photothermal thermography using thermal wave field interference for subsurface defect characterization

Abstract

The coherent superposition of two anti-phased thermal wave fields creates a zone of destructive interference which is extremely sensitive to the presence of defects without any reference measurements. Combining a high power laser with a spatial light modulator allows modulating phase and amplitude of an illuminated surface that induces spatially and temporally controlled thermal wave fields. The position and depth of defects are reconstructed from analysis of the amplitude and phase of the resulting photothermal signal. The proposed concept is experimentally validated and supported by numerical modeling.