The optical mobilities of particles in a cross-type particle separation system were measured numerically and experimentally. Three particles were chosen to test the effects of optical mobility, namely polystyrene latex (PSL), polymethylmethacrylate (PMMA) and silica particles. The particles, which had the same optical mobility, showed identical behavior even though their sizes and refractive indices were very different. The optical mobility was validated by measuring the distance each particle was deflected by the radiation force.
The Cross-type Optical Particle Separation system can sort micro particles continuously using loosely focused laser beam perpendicular to the direction of a flow in a micro channel. When micro spheres suspended in a flow meet the laser beam, they are pushed by a scattering force in the direction of the laser beam. While passing the laser beam zone, the position of the particle changes; after the zone, the particle is delivered by the flow in analysis districts, remaining its position. The pushed distance is defined as retention distance and we can classify micro particles by the difference of the retention distances. In contrast to the previous studies which separate micro spheres according to only a physical property, radius or the index of refractive of micro beads, micro spheres were first separated by the more accurate standard, optical mobility. With this study, we also demonstrated that the micro beads of the same optical mobility have the same retention distance.