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

Georges Brügger,Juan José Sáenz,Luis S Froufe-Pérez,Frank Scheffold

doi:10.1038/ncomms8460

Abstract

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 systems.

Highlights

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
The familiar isotropic dispersion forces between neutral objects arise from random electromagnetic waves generated by equilibrium quantum and thermal fluctuations[1,2,3,4]
Using optical tweezers as a gauge, we present experimental evidence for the predicted isotropic attractive interactions between dielectric microspheres induced by laser-generated, quasi-monochromatic random light fields

Summary

Introduction

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. We show, both theoretically and experimentally, that dispersion forces between small colloidal particles can be induced and controlled using artificially created fluctuating light fields. This can potentially be useful to anneal defects in periodic structures such as photonic crystals, to increase the effective temperature by optically shaking particles or to stabilize non-equillibrium phases such as supercooled liquids and, in general, to control the self-assembly and phase behaviour of colloidal particle assemblies on nano- and mesoscopic length scales[6,7]

Methods

Results

Conclusion