We use the three-dimensional time-dependent Schrödinger equation (3 D-TDSE) to calculate angular electron momentum distributions and photoelectron spectra of atoms driven by spatially inhomogeneous fields. An example for such inhomogeneous fields is the locally enhanced field induced by resonant plasmons, appearing at surfaces of metallic nanoparticles, nanotips, and gold bow-tie shaped nanostructures. Our studies show that the inhomogeneity of the laser electric field plays an important role on the above-threshold ionization process in the tunneling regime, causing significant modifications on the electron momentum distributions and photoelectron spectra, while its effects in the multiphoton regime appear to be negligible. Indeed, through the tunneling above-threshold ionization (ATI) process, one can obtain higher energy electrons as well as a high degree of asymmetry in the momentum space map. In this study we consider near infrared laser fields with intensities in the mid- ${10}^{14}$ W/cm${}^2$ range and we use a linear approximation to describe their spatial dependence. We show that in this case 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 fully supported by their classical counterparts.

• Received 20 January 2013

DOI:https://doi.org/10.1103/PhysRevA.87.063833