Tunable two-photon excited luminescence in single gold nanowires fabricated by lithographically patterned nanowire electrodeposition

The two-photon excited luminescence (TPEL) of single gold nanowires was investigated under far-field illumination with picosecond pulses. These nanowires, having a rectangular cross-section, a precisely defined thickness, and millimeter-scale length, were prepared by using the lithographically patterned nanowire electrodepostion (LPNE) technique. The TPEL from these wires was investigated as a function of wire thickness. It is found that the optical properties of the wire are dominated by the transverse surface plasmon resonance, which enhances the two-photon absorption process and subsequent emission in the polarization direction of the plasmon mode. Upon tuning the thickness of the wire from 74 to 25 nm, an enhancement of 3 orders of magnitude in the TPEL was observed. The TPEL tunability is found to be consistent with the geometry-dependent field concentration at the metal surface as predicted by the lightning rod model.