Optical sorting due to optical binding

Abstract

When several particles are illuminated by intense laser fields there exist also additional optical forces between the particles induced by scattered fields. This effect is called optical binding and the particles due to their mutual forces induced by light may create optically bound structure. As these forces are of second order (in comparison to forces induced by the incident fields) they are very sensitive to size or shape of the particles. We have previously experimentally studied the optical binding in the configurations employing two counter-propagation Bessel beams. These results were sufficiently supported by our numerical simulations (Coupled dipole method CDM). We study how the difference of sizes of two spherical particles influences their spatial stable separation. Even small changes in the limits of particle-size distribution of used particles may lead to experimentally verifiable differences. The intensities of the two beams must be also tuned to achieve sufficient stability of the whole couple in the experimental sample. By variation of mutual intensities we may also move the couple along the common optical axis. Another results may serve for detection of particles of different composition or shape. Very exciting configuration of ”Optical tractor beam” offers another and simple means of optical sorting. Our numerical results indicate that the behaviour is very sensitive to particles size. Here we present numerical studies how the sizes of individual particles (within the range of the particle-size distribution) influences the particles dynamics in various optical trapping configurations.