Nondimensional analysis of particle behavior during cross-type optical particle separation.

A nondimensional analysis of particle behavior during cross-type optical particle separation was performed. A new dimensionless number, S, was defined as the ratio of the optical force to the viscous drag force, and the effects of varying S on particle motion were examined. For large S, the particles undergo acceleration, deceleration, and release as they pass through the laser beam. The retention distance is much longer for large S than for small S. In addition, the effects on particle behavior of varying the wavelength of the laser beam, the particle size, and the index of refraction of the particles were investigated. Furthermore, an analytical expression of the retention distance for large S was validated.