The exploitation of the plasmonic response of metals for optical trapping applications may be divided into two broad categories. The first is to use the (LSPs) supported by metallic nanoparticles, which we have discussed in Section 3.9, to enhance their mechanical reaction to the fields and thereby enable optical trapping. The second is to use the (SPPs) supported by nanostructures on a substrate to generate enhanced fields over a small volume, where particles can be more effectively trapped, as we have seen in Subsection 12.4.4. The distinction between SPPs and LSPs is illustrated in Fig. 22.1. SPPs are the propagating electromagnetic surface waves arising from the excitation of a collective oscillation of the free electrons in a thin metal film, i.e., a quasi two-dimensional metallic structure that is nanoscale in one dimension only; since a SPP is an evanescent mode, it must be excited by an evanescent electric field, which is typically achieved using the Kretschmann geometry. LSPs, instead, are associated with excitations of oscillations in the bound electrons of metallic nanoparticles, or nanovoids within a metallic substrate, and can be directly excited with a propagating field. In this Chapter we review a number of optical trapping and manipulation experiments in which plasmonic force enhancement plays a crucial role.
22.1 Plasmonic nanoparticles
22.2 Plasmonic substrates
22.3 Plasmonic apertures
22.4 Further reading
References
Figure 22.1 — Plasmonic response of metal nanostructures
Figure 22.2 — Trapping of plasmonic nanowires
Figure 22.3 — Trapping of plasmonic nanoparticles
Figure 22.4 — Optical binding induced by surface plasmons
Figure 22.5 — Plasmonic optical tweezers
Figure 22.6 — Optical traps based on plasmonic nanoantennas
Figure 22.7 — Optical traps based on plasmonic nanoapertures