This paper presents a method to measure nanometric displacement fields using digital speckle pattern interferometry, which can be applied when the generated correlation fringes show less than one complete fringe. The method is based on the evaluation of the correlation between the two speckle interferograms generated by both deformation states of the object. The performance of the proposed method is analyzed using computer-simulated speckle interferograms. A comparison with the performance given by a phase-shifting technique is also presented, and the advantages and limitations of the proposed method are discussed. Finally, the performance of the proposed method to process real data is illustrated.
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Dynamic deformation measurement with 2-frame phase-shifting speckle interferometry based on speckle statistics and wavefront multiplexing.
Rev Sci Instrum
September 2024
State Key Laboratory for Manufacturing Systems Engineering, School of Instrument Science and Technology, Xi'an Jiaotong University, Xi'an, Shaanxi 710049, People's Republic of China.
Phase-shifting speckle interferometry could achieve full-field deformation measurement of rough surfaces. To meet the dynamic requirement and further improve the accuracy, a two-step synchronous phase-shifting measurement system is established based on the polarization-sensitive phase modulation ability of a liquid crystal spatial light modulator; by multiplexing the reference wavefront, an accurate phase shift is generated between two independent recording channels, and a common-path self-reference vortex interference structure is built for precise spatial registration. Meanwhile, according to the speckle statistical principle, a novel two-frame phase-shifting algorithm as well as a two-step spatial registration strategy is presented to strengthen the robustness of intensity and position differences caused by spatial-multiplexing; thereby, accurate transient deformation can be directly obtained from phase-shifting speckle interferograms recorded before and after deformation.
View Article and Find Full Text PDFArticle Synopsis
- - The paper presents an advanced method for measuring three-dimensional deformations using the phase and amplitude of speckle fields, which helps in determining out-of-plane and in-plane deformations, respectively.
- - It utilizes a polarization camera to simultaneously capture a 3-step phase-shifting interferogram and a speckle gram, applying optimal polarization states for enhanced measurement accuracy.
- - Results show that this optimized strategy significantly improves the quality of deformation measurements, with experiments confirming its effectiveness for real-time dynamic thermal deformation applications.
What we believe to be a new electronic speckle pattern interferometry (ESPI) configuration is being developed for simultaneous three-dimensional deformation measurements. In this ESPI system, two pairs of symmetrical illuminating arrangement with dual-wavelength lights were used to independently sense two in-plane deformation components, one Michelson interferometer-based set illuminating with the other wavelength light was utilized to measure out-of-plane deformation. The color speckle interferogram was split into four sub-patterns by a prism, three of them were filtered by three different bandpass dichroic filters and recorded by one monochrome camera.
View Article and Find Full Text PDFOptimizing the internal phase reference to shape the output of a multimode optical fiber.
PLoS One
September 2023
Istituto Italiano di Tecnologia, Center for Biomolecular Nanotechnologies, Arnesano, Italy.
Article Synopsis
- Pre-shaping light for multimode fibers allows for innovative imaging techniques by controlling amplitude distributions at the fiber's tip, which involves analyzing a scrambled light pattern created by the fiber.
- Recent methods utilizing an internal reference beam have shown improved stability in interferometric setups, but criticisms arise regarding their influence on measurement accuracy and potential "blind spots."
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An accurate dynamic 3D deformation measurement method realized by the combination of phase-shifting speckle interferometry and speckle correlation is proposed. By converting the speckle field and the reference field into a circular polarized and linear polarized state, the three-step phase-shifting speckle interferograms and one specklegram were recorded directly and simultaneously within a single image by using a polarization camera. Then, the out-of-plane deformation was demodulated from the synchronous phase-shifting fringe patterns, and the in-plane deformation was measured by performing correlation calculations by using specklegrams with the effect of the reference field ignored.
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