Controlled spatiotemporal excitation of metal nanoparticles with picosecond optical pulses

We discuss realistic finite-difference time-domain simulations of chirped optical pulses interacting with silver nanowires and cone-shaped nanoparticles. These systems are differently shaped and larger than those previously studied [M. I. Stockman, S. V. Faleev, and D. J. Bergman, Phys. Rev. Lett. 88, 067402 (2002)], but still allow for localized hot spots near the metal surfaces to be generated and controlled in a spatiotemporal manner. The control is made possible by chirping the pulses such that the effective frequency passes through surface plasmon resonances associated with different spatial regions of the nanostructure over the course of time. We demonstrate how this leads to counterintuitive, negative group velocities in some situations. The control is shown to scale with pulse duration from approximate to150 fs to at least approximate to2200 fs=2.2 ps, and we anticipate it to scale to longer durations. We further show that the response of such nanostructures to chirped pulses can provide a means of encoding or decoding optical signals, which could be verified experimentally.