Measurement of in-plane displacements using the phase singularities generated by directional wavelet transforms of speckle pattern images

Abstract

We present a method to determine micro and nano in-plane displacements based on the phase singularities generated by application of directional wavelet transforms to speckle pattern images. The spatial distribution of the obtained phase singularities by the wavelet transform configures a network, which is characterized by two quasi-orthogonal directions. The displacement value is determined by identifying the intersection points of the network before and after the displacement produced by the tested object. The performance of this method is evaluated using simulated speckle patterns and experimental data. The proposed approach is compared with the optical vortex metrology and digital image correlation methods in terms of performance and noise robustness, and the advantages and limitations associated to each method are also discussed.

Splitting, generation, and annihilation of phase singularities in non-coaxial interference of Bessel–Gaussian beams

“…The displacement relative to the beam size is defined by d w, d = while the arbitrary stretching coefficient is a 0.5 = and beam width is w 2 2 . s = By observing where the real and imaginary zero-contour lines intersect or the convergence points of the isophase lines in figure 1, we can summarize the location distribution of the singularity [52][53][54]. Meanwhile, the positive or negative sense of the charge can be judged according to the direction of phase change in the phase diagram [55].…”

Phase discontinuities induced scintillation enhancement: coherent vortex beams propagating through weak oceanic turbulence

“…Looking back on these researches, those who focused on the evolution behaviors of screw dislocations affected by initial optical fields or external perturbations accelerate the development of various applications of optical vortices in adaptive optics [15], optical vortex field manipulation [16] and optical measurement [17]. Further researches on the joint influence aimed to reduce the impact of external perturbations through exploring appropriate forms of initial optical fields [18].…”

Simple method for simultaneously measuring the magnitude and direction of 2D in-plane displacement in white-light speckle photography

“…A nanoscale displacement of up to 120 nm was detected with a standard deviation of 1.2 nm. By replacing optical vortex filtering with two directional wavelet transform to generate phase singularities, Vadnjal et al [48] developed a method called phase singularities crossing points (PSCP), which was more insensitive to the experimental environment and more robust with less calculating amounts than OVM. The measured displacements were approximately 200 and 13 μm.…”