Ultrafast Nanoplasmonic Photoelectron Dynamics Between the Multiphoton and Strong-Field Regimes with Tunable IR Excitation

We examined transitions between multiphoton-induced photoemission and strong-field tunnelling of electrons at the surface of gold nanoparticles using infrared femtosecond pulses between 800 nm and 2.4 µm with our newest experiments. In addition to the observation of non-adiabatic tunneling [1], we establish the theoretical background of plasmonic excitation in the infrared range, calculate spectra by solving the time-dependent Schrödinger equation (TDSE), and then verify the predictions with experimental results.