Diffraction of ultrashort pulse on a nanoscale conductive cone

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 appropiate 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 angle 0.1, distances ri = 1000 nm and rf = 250 nm. For a pulse with a chirp β = -0.013 fs1, pulse duration becomes shorter and changes from 32 fs to 18.8 fs, and field amplification is equal to 42.7.