Recent advances in dynamic speckle metrology: vortex analysis, numerical models and applications

H.J. RABAL, G.H. SENDRA, R. ARIZAGA, M. TRIVI

La Habana, Cuba

Conferencia; VI Workshop on Laser Technology TECNOLÁSER 2009 y II Reunión Internacional Óptica, Vida y Patrimonio, International Topical Meeting of International Commission for Optics (ICO); 2009

Dynamic speckle provides a comparatively economic tool for the non intrusive non destructiveassessment of some biological and industrial processes that is not very involved from the experimental point of view, is not very expensive and in some cases can be performed with equipment usually available in laboratories. It has been applied for blood perfusion measurements and paint drying evolution monitoring where commercial equipment are already available. Besides, several other phenomena have been successfully tested such as bacterial chemotaxis, seeds viability, measurement of vitreous and floury phases proportions, bruising in fruits, cookies and ice cream time evolution, etc. Activity images algorithms have been developed to show loci of similar activity: spectral bands, Hurst coefficient, wavelets entropy, fuzzy granularity and several others. These processings require the acquisition of stacks of images that adequately sample the evaluated process in the time domain. Dynamic speckles due to very slow processes, such as for example, corrosion, efflorescence, atmospheric turbulence, lack adequate tools for their evaluation. We have developed a numerical model for the simulation of those phenomena in some hitherto no contemplated situations including the possibility of changing the focusing and the curvature of the illuminating wavefront to permit the evaluation of the model in some theoretically and experimentally known situations. Optical vortices, which are singularities of the wave field where the phase is not defined, have recently been shown to provide excellent tools for measurements of quasi static deterministic displacements with, in some cases, nanometric precision. Then, we applied optical vortices, both numerically and experimentally, to look for speckle activity measures. As the numerical treatment of the vortices requires the use of a complex signal we filtered the intensity images with Laguerre-Gauss filters and used the core features of the vortices to identify homologous pairs in successive images and follow their evolution along time. As vortices are sparce we introduced numerical modifications to generate additional vortices in arbitrarily chosen positions. This possibility broadens the applicability of the technique suggesting new fields of application, such as the increase of resolution in the register of succesive images of dynamic phenomena, as in medicine or astronomy. The possibility of 3D contouring and of aberrations corrections are also envisaged.