Particulate Mueller matrix polarimetry

• The Mueller matrix measurement of individually suspended particles in water is achieved for the first time. • Microplastics and Microalgae can be effectively classified using particulate Mueller matrix polarimetry. • Particulate Mueller matrix polarimetry has great impacts on environmental monitoring and governance. Probing the suspended particles in natural water is significant for environmental monitoring and ecological research, such as early warning of water blooms and assessment of water quality. In this article, a conceptual Mueller matrix measurement method for individual suspended particles is proposed by simultaneously measuring the polarization states of the illuminating and scattered light. This so-called particulate Mueller matrix polarimetry (PMP) based on polarized light scattering at 120° is successfully achieved for the first time, and its performance and signal processing are revealed in detail. The physical properties and polarization features of suspended particles can be effectively obtained. Experiments with standard particles, different microplastics, and marine microalgae show that these particles can be effectively classified using PMP powered by the convolutional neural network. This presented laboratory system can serve as the proof-of-concept setup of new instrumentation for applications onboard or underwater.