Optical trapping in the presence of higher order mode sources and interactions

The force fields produced by higher order mode (HOM) TM^en1 sources are investigated analytically and numerically. Their application to optical manipulation and trapping is emphasized. It is found that the strong reactive fields excited by these advanced HOM nanoantennas significantly enhance both the gradient and near-field absorption-scattering forces, as well as increase the range of attraction of those absorption-scattering forces. Moreover, the impact on these force fields by the excitation of HOMs in a nanoparticle is addressed. These results are used to demonstrate the theoretical possibility of the generation of tractor beams by highly subwavelength sources on resonant dipolar nanoparticles. The analysis reveals that the associated attractive forces can be enhanced by several orders of magnitude before the HOMs induce any noticeable degradation of the radiation efficiency. The practical implementation of HOM TM^en1 sources by means of active core-shell resonators, as well as their potential for the self-induced trapping of fluorescent molecules, is also addressed. (paper)