  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 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 systems.
