Measurement systems for online nondestructive full-field three-dimensional (3D) displacement based on the single-shot and multiplexing techniques attract more and more interest, especially throughout the manufacturing industries. This paper proposes an accurate and easy-to-implement method based on an electronic speckle pattern interferometer (ESPI) with single illumination-detection path to realize the online nondestructive full-field 3D displacement measurement. The simple and compact optical system generates three different sensitivity vectors to enable the evaluation of the three orthogonal displacement components. By applying the spatial carrier phase-shifting technique, the desired information can be obtained in real time. The theoretical analysis and the measurement results have proven the feasibility of this ESPI system and quantified its relative measurement error.

A temporal electronic speckle pattern interferometry (ESPI) system is proposed for in-plane rotation measurement. The relationship between the rotation angle and the phase change distribution is established and the rotation direction is indicated by the sign of the partial differential of the phase change distribution. Temporal phase modulation is applied in the proposed symmetric illumination ESPI system. The phase is recovered by the temporal intensity analysis method which uses the temporal evolution history of the light intensity. The system can perform dynamic measurements and provide results in off-line real-time. Preliminary experiments were carried out with a continuously rotating target to show the feasibility and the dynamic feature of the temporal ESPI system. At present, the mean absolute error of the experiment is 0.39 arcsec.

A real-time, dual-sensitive shearography system using a single-wavelength laser was developed for simultaneous and dynamic in-plane and out-of-plane strain measurements. The shearography system is capable of measuring crack-tip deformation fields quantitatively. A spatial multiplexing technique based on Fourier transform is employed for simultaneous and dynamic multi-component phase retrieval. Two slit spatial filters and a common-path shearing interferometer are used to obtain an improved phase quality for crack-tip deformation measurements. Mode-I fracture experiments under three-point bending were conducted to validate the feasibility and the capability of this method.

Electronic speckle-pattern interferometry (ESPI) is a powerful tool for precise, full-field, and non-contact contouring of optically rough surfaces. Due to the interferometric principle, the sensitivity of ESPI is directly related to the involved wavelengths and is thereby a global parameter. Surfaces with a broad variation of phase gradients, as, for instance, a target with both smooth and comparatively steep areas, result in just partially resolvable fringe interferograms. In recent studies, spatial light modulators (SLMs) have been implemented to adapt the interferometric reference phase front to the measurement task and broaden or squeeze the fringe spacing locally in critical areas. This method is limited by diffraction effects, observable for all types of phase-only SLMs. We demonstrate a straight-forward model, describing the diffraction-based intensity distortions occurring in interferograms after wavefront adaptation. The aim is to characterize the intensity distortions by means of the proposed model and minimize their impact, especially with regard to phase-only spatial light modulation in ESPI. For validation, the modeled behavior of SLMs is compared to the experimental results, obtained for two different SLM designs. Finally, experiments are presented, which demonstrate a successful adaptation of the interferometric reference phase front in compliance with the boundary conditions determined by the model.

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