Nanofocusing of Ultrafast Surface Plasmon Polariton Pulses with a Gold-Tapered Tip and Applications to Nonlinear Nanoimaging

Abstract

Nano-focusing of grating-coupled surface plasmon polariton (SPP) pulses along a tapered gold tip is simulated by a finite-differential time-domain (FDTD) method to optimize the diffraction grating structure fabricated on the tip. We experimentally demonstrate the enhancement of nanofocused ultrafast SPP pulse intensity with optimization in the wave front and the spectral phase of the incident femtosecond laser pulses to the grating structure. We also experimentally achieve ultrafast nonlinear imaging using the nanofocused ultrafast SPP pulse at the tip apex.