Sizing submicron particles from optical scattering data collected with oblique incidence illumination

Area of Science:

• Environmental Science
• Optical Physics
• Analytical Chemistry

Background:

• Submicron particles are crucial in various ecosystems (aqueous, terrestrial, atmospheric).
• Accurate quantification of these particles is essential for environmental monitoring and research.
• Existing methods may have limitations in range or applicability.

Purpose of the Study:

• To develop and validate a novel measurement system for sizing submicron particles using visible light.
• To assess the system's accuracy and sensitivity across different particle properties.
• To explore the potential of this technology for real-world environmental applications.

Main Methods:

• A prototype system was designed to collect multi-directional scattered light from individual particles.
• Oblique illumination was used to capture scattered light over a wide angular range (forward and backward).
• A ratio of integrated forward to backscattered light was calculated and correlated with particle size.

Main Results:

• The system accurately resolved particle sizes in the 0.1 to 0.8 μm range, validated with polystyrene spheres.
• Simulations and tests showed the forward-to-backscatter ratio has a monotonic dependence on particle size.
• The technique demonstrated relative insensitivity to the particles' relative refractive index.

Conclusions:

• The developed system offers a promising method for accurate submicron particle sizing.
• Its robustness to refractive index variations enhances its applicability across diverse environmental samples.
• Further research with environmentally relevant specimens is needed to optimize the system for pragmatic field use.