Ricardo Arizaga

Speckle time evolution characterization by the co-occurrence matrix analysis

Abstract We describe some aspects of the measurement of dynamic speckle activity. We propose the use of the co-occurrence matrix of the time history of the intensity of a speckle pattern. Then we suggest a measure of the activity based on the use of one of its second order moments. Some numerical simulations were performed for testing purposes. The method was applied to the study of the drying of paint and was compared with gravimetric measurements. Experimental results obtained are shown and a good correlation is obtained.

Display of local activity using dynamical speckle patterns

We present a display to distinguish loci of equal activity in samples showing dynamic speckle patterns. Regions differing in their activity are shown as different gray levels. We define the generalized differences and the weighted generalized difference operations and we compare the results with previously reported methods. Results obtained with seeds are shown.

Bio-speckle assessment of bruising in fruits

The dynamic speckle patterns or bio-speckle is a phenomenon produced by laser illumination of active materials, such as a biological tissue. Fruits, even hard peel ones, show a speckle activity that can be related to maturity, turgor, damage, aging, and mechanical properties. In this case, we suggest a bio-speckle technique as a potential methodology for the study of impact on apples and the analysis of bruises produced by them. The aim is to correlate physical properties of apples with quality factors using a non-contact and non-invasive technique.

Application of dynamic speckle interferometry to the drying of coatings

In this work a new tool to study the drying of paints, based on an optical technique known as dynamic speckle interferometry is presented. The basic concepts of the technique are described and applied to the drying process of white solvent-borne and white water-borne paints (latex paint) following the time evolution of the activity of dynamic speckle patterns. For processing the data an alternative method based on the use of the second-order moment of the modified co-occurrence matrix of the time history of its intensity was used. The experimental results obtained were compared with the gravimetric technique and the resulting curves from the speckle-time evolution compared favorably with gravimetric drying curves. The results were also discussed on the basis of the knowledge of the coating drying process and factors related with the surface properties. Dynamic speckle interferometry seems to be a useful technique for assessing the time evolution of surfaces and, its sensitivity to refractive index changes helps to determine the start of different stages during the drying of latex paints. The dynamic speckle method tests mainly the activity on the surface and the measurements seem to confirm that the initial stage of drying is like a pure solvent. Finally, the study of different aspects of the drying process using this technique is proposed.

Decomposition of biospeckle images in temporary spectral bands

We present a method of analysis of images of dynamic speckle based on the filtering in frequency bands of the temporary history of each pixel. Butterworth filters are applied to the temporary evolution, and different images are constructed showing the energy in each frequency band. Different degrees of activity of the sample in study, presumably attributed to different origins, are found. The method is exemplified with images of bruising damage in fruits and of biological activity in germinating corn seeds. It is found that the activity in the bruised region of an apple differs from the activity of healthy regions in a certain characteristic frequency range. The activity of the embryo can also be distinguished from that of the endosperm in corn seeds during germination.

Transient phenomena analysis using dynamic speckle patterns

The full width at half maximum (FWHM) is sometimes used to characterize the autocorrelation function of the time history of a speckle pattern. We propose to include more autocorrelation points to diminish the variability of the measurement. The width of the equivalent rectangle (WER) and the X*LOG X measurements are defined and some simulations and experimental results obtained are shown.

Analysis of bacterial chemotactic response using dynamic laser speckle

Chemotaxis has a meaningful role in several fields, such as microbial physiology, medicine and biotechnology. We present a new application of dynamic laser speckle (or biospeckle) to detect different degrees of bacterial motility during chemotactic response experiments. Encouraging results showed different bacterial dynamic responses due to differences in the hardness of the support in the swarming plates. We compare this method to a conventional technique that uses white light. Both methods showed to be analogous and, in some cases, complementary. The results suggest that biospeckle processed images can be used as an alternative method to evaluate bacterial chemotactic response and can supply additional information about the bacterial motility in different areas of the swarm plate assay that might be useful for biological analysis.

Fully digital encryption technique

We propose an alternative fully digital encryption technique based on using the Fourier transform of the original object to be processed and a speckled reference wave as encryption mask. Once encrypted, the Fourier transform spectrum of the object is holographically stored. The original-data recovering is performed by digital reconstruction using the same encryption mask, which is also holographically stored. Quality of reconstructed data is evaluated as a function of the sensed encrypted data. Computer simulations and experimental results are presented to demonstrate the method.

Numerical model for dynamic speckle: an approach using the movement of the scatterers

Dynamic speckle or biospeckle is a phenomenon generated by laser light scattering in biological tissues and it is also present in some industrial processes where the surfaces exhibit some kind of activity. In this work we present some results of a numerical model to describe the time history of a dynamic speckle pattern considering very simplified situations. In this case we simulated only the movement of the scatterers, and the obtained results are in agreement with some of the expected from the theory and qualitatively with the experimental results outlined in previous works. Also, we tested the first order statistics of the spatial speckle, the Briers contrast of the time varying part and the moment of inertia of the co-occurrence matrix.

Vortex analysis in dynamic speckle images

Optical vortex analysis has become an important tool in optical metrology. It has been shown to be able to measure small displacements with up to nanometric precision. We analyze optical vortex behavior in dynamic speckle patterns with the boiling phenomenon. We first study translational patterns with boiling and we find the limitations of the optical vortex metrology. Pure boiling patterns are also evaluated and we find a quantitative descriptor for the activity. We also observe that vortices exhibit a Brownian motion in pure boiling patterns. Numerical and experimental results are shown.