Off-Resonant Two-Photon Absorption Cross-Section Enhancement of an Organic Chromophore on Gold Nanorods.

Surface-plasmon-initiated interference effects of polyelectrolyte-coated gold nano-rods on the two-photon absorption of an organic chromophore were investigated. With polyelectrolyte-bearing gold nanorods of two, four, six, and eight layers, the role of the plasmonic fields as function of distance on such effects was examined An unusual distance dependence was found: enhancements in the two-photon cross-section were at a minimum at an intermediate distance, then rose again at a further distance. The observed values of enhancement were compared to theoretical predictions using finite element analysis and showed good agreement due to constructive and destructive interference effects.