Optical EngineeringNondestructive testing with thermal waves using phase-shifted temporal speckle pattern interferometry
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A temporally modulated IR lamp is employed to heat the surface of a flawed plate and the resulting out-of-plane thermoelastic deflection is monitored using phase-shifted temporal speckle pattern interferometry. The speckle interferograms are continuously recorded by means of a high-speed digital camera with temporal phase shifting carried out by a Pockels cell synchronized with it. Temporal phase unwrapping through sequences of several hundreds of frames enables the determination of time-varying absolute displacement maps. Experimental results illustrate the possibilities of this novel nondestructive testing technique.