Propagation analysis of space-time surface plasmon polariton wave packet excited by light irradiation on nanobeam structure

We investigate space-time surface plasmon polariton (ST-SPP) wave packet, a conceptual correspondence of a surface-electromagnetic wave to the space-time wave (ST wave) that is excited on a metal surface through a light-SPP coupling at a nano-scaled ridge. In a framework of the finite-difference time-domain (FDTD) method, a pulsed excitation light was constructed by using a couple of hundred plane waves with different frequencies whose intensity and incident angle were determined to satisfy the conditions for generating ST wave according to the dispersion relation of SPP on the metal surface. The ST-SPP WP launched from the nano-ridge exhibited propagation invariance and tunability of the group velocity.