Applicability of Free Propagation Configurations in Dynamic Laser Speckle

Dynamic laser speckle (DLS) is a well-established sensing technique for monitoring activity in biological and non-biological samples. While traditionally reliant on macro-lens (imaging speckle) systems, this study investigated the reliability of a macro-lensless, free-propagation (objective speckle) configuration to reduce cost and to enable its compactness. We evaluated this simplified setup using homogeneous (drying coatings) and heterogeneous (ionic solutions and seeds) samples, comparing results against traditional imaging speckle configurations via numerical and graphical indices. Findings demonstrated that free propagation is not only a viable alternative for homogeneous materials but can outperform macro lens-based systems in specific heterogeneous contexts. These results suggest that removing the macro lens offers a robust, cost-effective, and potentially superior architecture for DLS activity monitoring.