N. Budini

Extraction of dynamic speckle activity information from digital holograms

Abstract. In this work we show how dynamic speckle information can be extracted directly from digital holograms. This allows improving the analysis and characterization of dynamic phenomena by combining dynamic speckle with digital holographic interferometry measurements. We have studied the drying process of paint coatings, which is a typical study case in the field of dynamic speckle characterization, since the speckle activity (SA) of drying coatings is known to decay smoothly as a function of time. We recorded both holograms and speckle images during the process. In this way, we could compare the evolution of global SA calculated from speckle images by a standard method with the evolution of speckle correlation extracted directly from the holograms. The results obtained from both methods have shown to be in good agreement.

Characterization of drying paint coatings by dynamic speckle and holographic interferometry measurements

In this work we implemented dynamic speckle and holographic interferometry techniques to characterize the drying process of solvent-based paint coatings. We propose a simple way to estimate drying time by measuring speckle activity and incrementally fitting experimental data through standard regression algorithms. This allowed us to predict drying time after about 20-30 min of paint application, which is fast compared to usual times required to reach the so-called tack-free state (≈2  h). In turn, we used holographic interferometry to map small thickness variations in the coating surface during drying. We also demonstrate that results obtained from both techniques correlate with each other, which allows us to improve the accuracy of the drying time estimation.

Biospeckle Activity Evolution of Strawberries

Fil: Mulone, Cecilia. Universidad Tecnologica Nacional. Facultad Regional Parana; Argentina

Dynamic speckle study of microbial growth

In this work we present a characterization of yeast dynamic speckle activity during growth in an isolated agar culture medium. We found that it is possible to detect the growth of the microorganisms even before they turn out to be visible. By observing the time evolution of the speckle activity at different regions of the culture medium we could extract a map of the growth process, which served to analyze how the yeast develops and spreads over the agars medium. An interesting point of this study concerns with the influence of the laser light on the yeast growth rate. We have found that yeast finds hard to develop at regions with higher laser light illumination, although we used a synchronous system to capture the speckle pattern. The results obtained in this work would serve us as a starting point to fabricate a detector of growing microorganism colonies, with obvious interesting applications in diverse areas.

Analysis of small deflections by double-exposure digital holographic interferometry

We analyzed small deflections (~1 μm) of an opaque object by means of the double-exposure digital holographic interferometry technique, using an off-axis lensless Fourier holographic arrangement. The deflections were caused by heating the object with a flowing dc current. In our holographic arrangement, out-of-plane displacements of around 300 nm can be precisely detected by using a He-Ne laser as the coherent illumination source. However, this resolution could be improved by modifying the experimental setup or even choosing an appropriate object reference state. We briefly show the theoretical description of the technique and conduct experiments and simulations to test the results. Since the object we have studied in this work is a bimetallic strip, the obtained results point towards further research concerning precise temperature sensing devices.