Controlling dispersion forces between small particles with artificially created random light fields

Appropriate combinations of laser beams can be used to trap and manipulate small particles with optical tweezers as well as to induce significant optical binding forces between particles. These interaction forces are usually strongly anisotropic depending on the interference landscape of the external fields. This is in contrast with the familiar isotropic, translationally invariant, van der Waals and, in general, Casimir-Lifshitz interactions between neutral bodies arising from random electromagnetic waves generated by equilibrium quantum and thermal fluctuations. Here we show, both theoretically and experimentally, that dispersion forces between small colloidal particles can also be induced and controlled using artificially created fluctuating light fields. Using optical tweezers as a gauge, we present experimental evidence for the predicted isotropic attractive interactions between dielectric microspheres induced by laser-generated, random light fields. These light-induced interactions open a path towards the control of translationally invariant interactions with tuneable strength and range in colloidal systemsThis work was supported by the Swiss National Science Foundation through project numbers 132736 and 149867, and through the National Centre of Competence in Research Bio-Inspired Materials. J.J.S. acknowledges financial support by the Spanish MEC (grant number FIS2012-36113), Comunidad de Madrid (grant number S2009/TIC-1476-Microseres Program-) and by an IKERBASQUE Visiting Fellowship (J.J.S.