Single laser beam based passive optical sorter

We demonstrate experimentally a new method of sorting of colloidal particle suspension in wide single laser beam. The sorting is performed in a realization of a "tractor" beam a weakly focused laser beam that is retro-reflected under an oblique angle. In this configuration the lateral positions of particles dependent on the direction of linear polarization of the beam. Polarization rotation by 90 degrees changes the sign of the lateral optical force acting upon particles of certain properties and such particles are propelled in the opposite direction. This approach provides surprisingly efficient way of passive sorting of tens of particles by pure switching the beam polarization.