Nanoparticle manipulation through inter-particle optical forces and torques

Recently, emerging from studies based on quantum electrodynamics, it has been shown possible to significantly modify the form and magnitude of inter-particle forces by the throughput of intense laser light. This paper identifies these laser-induced forces as being the result of coherent stimulated scattering by particle pairs. Such forces have the capacity to generate novel patterns of nanoscale response, entirely determined and controlled by the frequency, intensity, polarisation and other features of the laser input. Results are given, based on general calculations of the optical forces and torques operating between a pair of dielectric particles. It is subsequently shown, by further development of the analysis, that it is possible to address the case of a twisted (Laguerre-Gaussian) laser beam as the input radiation. Here, the results reveal additional and highly distinctive torques operating between pairs of nanoparticles. Significantly the results demonstrate that these laser-induced forces and torques can be either positive or negative according to conditions. As a consequence, new possibilities emerge for the optical control of nanoparticle ordering, clustering and trapping.