Improved transmission method for measuring the optical extinction coefficient of micro/nano particle suspensions

Extinction coefficient is fundamental to analyze radiative transport in micro/nano particle suspensions. In the traditional transmission method for measuring the extinction coefficient of particles in a cuvette, a reference system is used to compensate the influence of the cuvette and base fluid. However, the multiple reflections and refractions between the air/glass and liquid/glass interfaces cannot be sufficiently eliminated by using the reference system, and the induced measurement error increases significantly with increasing difference in refractive index between two neighboring media at these interfaces. In this paper, an improved transmission method is proposed to measure the extinction coefficient of micro/nano particles. The extinction coefficient of the particles is determined based on an optical model taking into account the multiple reflection and refraction at the glass/liquid interfaces. An experimental validation was conducted for suspensions with various mean particle sizes. By considering the higher-order transmission terms, the improved transmission method generally achieved high accuracy improvement over the traditional transmission method for extinction coefficient measurement, especially for the case with small optical thickness of particle suspensions. This work provides an alternative and more accurate way for measuring the extinction characteristics of micro/nano particle suspensions.