Controlling the dynamics of the plasmonic field in the nano-femtosecond scale by chirped femtosecond laser pulse

Arbitrary control of the electromagnetic field in femto-nano scale has attracted significant research attention in nano-photonics. Although the electromagnetic field controlled in femto-nano scale could be realized by illuminating metallic nanoparticles with femtosecond chirped laser pulses, the quantitative relation of the laser chirp and the temporal evolution of the plasmonic field hasn’t yet been fully revealed. Here, active control of the localized plasmonic field is demonstrated by a chirped femtosecond laser pulse in an asymmetric Au nano-cross system within nm-fs scale using the finite differential time domain method. The transferring of the plasmonic field between the two poles of the nanocross is determined by the laser chirp and exhibits linear dependence on the time interval between the corresponding plasmonic resonant frequencies dispersed in the chirped laser pulse. The arrival time and amplitude of the peak field from the plasmonic hot spot are determined by the superposition of the induced field excited by the on-resonant and off-resonant frequency components distributed in the chirped laser pulse. The peak field would arrive behind the resonant frequency component for sufficient oscillation of the localized field. This relative delay between the resonant frequency and field peak is influenced by the temporal distribution of the resonant frequency in the chirped pulse and the response of localized field interpreted by the damped harmonic oscillator model. This result demonstrates that larger near-field enhancement is determined by not only the temporal sequence of the frequency component modulated by chirp but also the temporal distribution of the resonant frequency.