Generation of ultrashort extreme-ultraviolet pulses by enhanced plasmonic near-fields in metallic nanoparticles

We investigate high-order harmonic generation in a metallic-nanoparticle-quantum-dot hybrid system. Driven by a moderate electric field intensity Guassian-shape few-cycle pulse which is chirped by a hyperbolic-tangent-form carrier envelope phase, the hybrid system can generate extreme-ultraviolet super-continuum harmonics (13.3 eV maximal photon energy) and isolated ultrashort pulses ( FWHM). Numerical simulation results reveal that the plasmonic field enhancement could extend the cutoff order and continuum region in harmonic spectra. The extension effect by plasmonic enhancement could be well understood theoretically by the semi-classical two-level atom model.