Self-referencing speckle pattern interferometry for deformation measurement in vibrating environments

Speckle pattern interferometry offers non-contact, high sensitivity, and full-field measurement, but in vibrating environments the object and reference beams follow separate paths, leading to random optical path difference fluctuations and severe degradation of fringe contrast. This study presents and experimentally validates a self-referencing digital speckle pattern interferometry system based on point diffraction. In this system, the reference beam is not derived from an independent source or an additional beam-splitting branch; rather, it is directly obtained from the object light scattered by the test specimen. A pinhole placed at the Fourier plane of a 4f system performs low-pass filtering, extracting a plane wave with uniform phase from the scattered object light to serve as the reference, thereby realizing a self-referencing configuration. This reference beam interferes with the original object light on the sensor of a polarization camera, and the pixelated polarizer array enables single-shot carrier phase shifting, allowing real-time phase extraction without mechanical scanning. Theoretical analysis shows that when the pinhole is strictly concentric with the aperture stop, the phase shift introduced by lateral object vibration to the reference beam is completely eliminated, while environmental vibrations act as common-mode disturbances on both beams and cancel out in the interference. Experimental comparisons between the proposed system and a conventional speckle pattern interferometer under no‑vibration and various vibration conditions (with different rotation motor speeds) reveal that under strong vibration, the phase fringes of the conventional system become completely indistinguishable, whereas the self-referencing system still yields a clearly resolvable interferometric phase map. Requiring neither a vibration isolation table nor a pulsed light source, the self‑referencing configuration exhibits significantly enhanced measurement stability in strong vibration environments, offering a reliable solution for industrial in‑situ inspection and field applications.