Particle Metrology and Classification Instrumentation Based on Dual-Wavelength Illumination and Modulated Polarization Detection

Understanding, detection, and identification of particles are of utmost importance in various industrial fields and environmental science. Here, we present a practical implementation based on polarization characterizations for particle metrology and classification. This platform utilizes dual wavelength illumination and a modulated detection configuration in order to meet the intrinsic safety requirements for energy-sensitive particle identification. A continuous mode laser with lower power is used to monitor the presence of particles, and at the same time, provides a cueing signal to trigger a second laser with relatively high power to measure the perpendicular and parallel components of the scattered light. In lieu of analyzing derived polarization ratios, our approach involves support vector machines (SVMs) to interrogate the raw data, which effectively circumvents the reduction of feature dimensionality, resulting in enhanced classification accuracy. A single aspheric beam homogenizer is then customized to achieve uniform particle illumination. The tunability of this homogenizer also permits great flexibility with the mechanical and aerodynamic design. The platform developed in this work allows concurrently measuring particle size and distribution, as well as accurate identification. The integrated platform developed in this study presents a multitude of advantageous features, encompassing intrinsic safety, accuracy, compactness, efficiency, and real-time sensing capability. These attributes position it as highly relevant for industrial applications that demand on-site or remote metrology and identification of energy-sensitive particles.