Above-threshold ionization by few-cycle spatially inhomogeneous fields

We present theoretical studies of above-threshold ionization (ATI) produced by spatially inhomogeneous fields. This kind of field appears as a result of the illumination of plasmonic nanostructures and metal nanoparticles with a short laser pulse. We use the time-dependent Schr\"odinger equation in reduced dimensions to understand and characterize the ATI features in these fields. It is demonstrated that the inhomogeneity of the enhanced plasmonic field plays an important role in the ATI process and it produces appreciable modifications to the energy-resolved photoelectron spectra. In fact, our numerical simulations reveal that high-energy electrons can be generated. Specifically, using a linear approximation for the spatial dependence of the enhanced plasmonic field and with a near-infrared laser with intensities in the mid ${10}^{14}$ W/cm${}^{2}$ range, we show it is possible to drive electrons with energies in the near-keV regime. Furthermore, we study how the carrier envelope phase influences the emission of ATI photoelectrons for few-cycle pulses. Our quantum mechanical calculations are supported by their classical counterparts.