Flaw detection using temporal speckle pattern interferometry and thermal waves

Abstract

This paper presents a temporal speckle pattern interferometry (TSPI) system which uses thermal waves to detect internal defects. The system allows the measurement of out-of-plane thermoelastic displacements generated when a specimen is locally heated with a temporally modulated CO₂ laser. The defects can be detected by observing the perturbations which appear in the induced displacement field. Displacements are determined from the calculation of the optical phase distribution using a temporal phase shifting method and temporal phase unwrapping. The description of the TSPI system is followed by the presentation of experimental results that demonstrate that the detectability of certain type of flaws is improved by the use of thermal waves.