Revisiting transverse optical binding

In their pioneering work, Burns et al. [Phys. Rev. Lett. 63, 1233 (1989)] discovered a laser-induced optical interaction between dielectric microparticles dispersed in water. This interaction occurred in the plane transversal to the laser beam and, interestingly, induced bound pairs of particles. Accordingly, the observed phenomenon was termed "transverse optical binding" (TOB). Burns et al. argued that TOB arises from coherently induced electric dipoles in the microspheres. Indeed, this explanation verified the experimental observation that the spatial periodicity of the TOB interaction matched the laser wavelength in water. However, relatively little experimental evidence has been provided, to date, for both the strength and functional dependence of this effect on the particle distance. In our study, we used an experimental method which allowed us to directly measure the TOB interaction. As a result, we found that this interaction is surprisingly long-ranged.