Encapsulated morphology measurement based on continuous-wave terahertz reflective off-axis digital holography

Terahertz nondestructive testing is an increasingly important technology in recent years. Compared with visible and infrared bands, terahertz wave can easily penetrate common nonpolar and nonmetal materials without ironize the sample because of low energy. Digital holography can reconstruct the quantitative amplitude and phase distributions of the object wavefront. We proposed a continuous-wave terahertz reflective off-axis digital holography to measure the morphology of encapsulated object. An experimental system was built using a 2.52 THz (118.83 μm) far-infrared gas laser 295-FIR and a pyroelectric array detector. The morphology of the metallic bookmark hidden behind the optically opaque materials such as polytetrafluoroethylene and Polypropylene plates were obtained by angular spectrum integral and phase unwrapping algorithm. It proves that THz digital holography is an effective nondestructive testing method.

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