DYNAMIC SPECKLE

Responsible:
- PhD. Myrian Tebaldi

Collaborators:
- Mg. Eng. Proff. Leandro Buffarini
- BSC. Nelly Cap
- Eng. Eduardo Grumel
- PhD. Damian Gulich

Historical review

Objects illuminated with coherent light take on a peculiar granular appearance called a speckle. If the surface is optically rough it evolves over time, the scattered light gives rise to a dynamic speckle pattern and its variation depends on the activity of the sample. Biological samples and other dynamic processes (blood flow, vibrations, etc.) show this behavior. Dynamic speckle or biospeckle can also be observed in non-biological industrial processes, including paint drying, corrosion and heat exchange. The visual appearance of the dynamic speckle diagram is similar to that of a boiling liquid. This activity occurs when the sample changes its characteristics due to the movement of the dispersion centers, changes in the optical path due to variations in the refractive index, changes in configuration or a combination of these situations.

The study of the temporal evolution of speckle patterns can provide an interesting tool to characterize the parameters involved in transient biological and industrial processes. Since 1996, many efforts have been made at CIOp, to assign numbers that characterize this biospeckle activity and that correlate favorably with alternative measurement methods of interest to the experimenter.

Several algorithms have been developed to characterize the dynamic activity of the speckle pattern using contrast analysis, accumulation of differences between images, spatial and temporal analysis of the speckle pattern, wavelet-based entropy, temporal spectral bands, etc. In these methods a qualitative evaluation of the phenomenon under study is presented. For quantitative measurements, the time history of speckle pattern (THSP) analysis with the autocorrelation function, the moment of inertia of the co-occurrence matrix, the structure function, the spatial variation of the phase and difference histogram methods. Numerical models based on the movement of the dispersion centers and an assessment of the spatial variation of the phase were also proposed.

The uses of biospeckle techniques aimed at the characterization of biological tissues and industrial processes were developed at CIOp. For example: seed viability, fruit damage, parasite mobility, fungal detection, chemotaxis in bacteria, paint drying processes, hydroadsorption in gels, foam evolution, etc. Some of these works were carried out in collaboration with groups from the Universities of Rosario (IFIR), Salta, the Center of the Province of Buenos Aires (Tandil), CIDEPINT (La Plata), the Universities of Lavras and Sao Paulo, Brazil, Catholic of Peru (Lima), of Antioquia, Colombia and of the Polytechnic Institute, Havana, Cuba.

 

Lines of research:

Projects in progress: