Figure 12.11 — Plasmonic traps Figure 12.11 — Plasmonic traps. (a) Set-up with which the first measurement of plasmon radiation forces was performed. (b) Kretschmann geometry to excite surface plasmons. (c) Patterned plasmonic optical traps filled with 4.88 μm-diameter polystyrene microparticles in the shape of the letters ‘SP’. (d) Plasmonic nanoantenna structure consisting of pairs of nanodots of height 90 nm, diameter 134 nm and separated by 200 nm. (e) Experimental set-up to observe trapping in the nanoantenna structure. The λ0 = 1064 nm laser beam excites a localised surface plasmon in the nanoantennas, which concentrates the field in the small gap between the nanodots. (f) Trajectory of a trapped 200 nm-diameter particle superimposed on an image of nanoantennas. The position fluctuations have a root-mean-square deviation of 18 nm.Figure (a) is reprinted from Volpe et al., Phys. Rev. Lett. 96, 238101. Copyright (2006) by the American Physical Society.Figures (b) and (c) are reprinted by permission from Macmillan Publishers Ltd: Righini et al., Nature Phys. 3, 477–80, copyright 2007.Figures (d)–(f) are reprinted by permission from Macmillan Publishers Ltd: Grigorenko et al., Nature Photon. 2, 365–70, copyright 2008.