  Surface plasmon polariton is collective oscillation of the free electrons at
metal dielectric interface. As a wave phenomenon, surface plasmon polaritons
can be focused using appropriate excitation geometry of metallic structures. We
theoretically demonstrate the possibility of controlling nanoscale short pulse
superfocusing based on the generation of radially polarized surface plasmon
polariton mode of conical metallic tip. Numerical simulation for femtosecond
pulse propagation along a silver nano-needle is discussed. The spatial
distribution for a near field strongly depends on a linear chirp of the laser
pulse which can partially compensate the wave dispersion. Field distribution is
calculated for different chirp values, opening angles and distances. For a
pulse with a negative chirp, pulse duration becomes shorter with amplification
~40.
