Abstract
In this paper, we present a model to account for the absorption of ultrafast laser pulse on a metallic tip and to calculate its induced hot carriers (or electrons) emitted from the surface over a wide range of operating condition from low (multiphoton absorption) to high (optical tunneling) laser field. The model self-consistently include the non-equilibrium heating of the electrons with time-dependent electron energy distribution and multiple-energy time-dependent tunneling process. A universal critical Keldysh parameter at the transition between the multiphoton absorption and optical tunneling regimes is obtained. The effect of the plasmonic enhancement at the tip at sub-10 fs laser pulses are also studied. It is found that at very short laser pulse (a few cycles), the classical photo-electric effect is not valid. For the plasmonic effect, there is a time delay between the plasmonic field and laser field, and thus the emission of electrons are lapsed than the laser field. The enhancement of electron emission due to the ultrafast laser induced plasmonic field at low field regime is also discussed.