Mechanism of the ordered particles arrangement in a concentration grating excited in the field of counter-propagating Gaussian beams

In the two-particle approximation, we consider the mechanism for the formation of an ordered arrangement of transparent spherical particles of small size in a concentration grating excited by the gradient force of counter-propagating Gaussian laser beams. This mechanism is due to the joint action of the transverse gradient force and the Coulomb force arising as a result of dipole-dipole interactions between particles.