Dynamic speckle deflectometry based on backward digital image correlation

Traditional phase measuring deflectometry locates the screen source point (SSP) using the sinusoidal fringe based phase extraction and unwrapping methods, which cannot realize dynamic measurement. And the digital image correlation based deflectometry needs at least 2 shots for surface reconstruction. We propose a single-shot dynamic speckle deflectometry (DSD) that locates the SSP by directly matching the captured single-shot speckle pattern with a computer synthesized speckle pattern. The theoretical basis is detailed. Numerical simulation is conducted to evaluate the validity and robustness of DSD with comparison to the fringe based approaches. The accuracy performance of DSD is quantified by measuring a glass piece, the surface result differs from that of interferometer 46.0 nm in root mean square. The dynamic motion of a wafer deformed by squeezing force is recorded by DSD, the squeezing force brings a shape deformation mainly in the form of astigmatism to the wafer surface.

Automated summary

Traditional phase measuring deflectometry and digital image correlation based deflectometry have limitations in dynamic measurement, while our proposed single-shot dynamic speckle deflectometry offers a solution with validated accuracy and robustness through numerical simulations and practical measurements.