Above-threshold ionization driven by few-cycle spatially bounded inhomogeneous laser fields

Abstract

In this work, we study the main features of the photoelectrons generated when noble gas atoms are driven by spatially bounded inhomogeneous strong laser fields. These spatial inhomogeneous oscillating fields, employed to ionize and accelerate the electrons, result from the interaction between a pulsed low intensity laser and bow-tie shaped gold nanostructures. Under this excitation scheme, energy-resolved above-threshold ionization (ATI) photoelectron spectra have been simulated by solving the one-dimensional (1D) time-dependent Schrödinger equation (TDSE) within the single active electron (SAE) approximation. These quantum mechanical results are supported by their classical counterparts, obtained by the numerical integration of the Newton-Lorentz equation. By using near-infrared wavelengths (0.8-3 μm) sources, our results show that very high energetic electrons (with kinetic energies in the keV domain) can be generated, far exceeding the limits obtained by using conventional, spatially homogeneous fields. This new characteristic can be supported considering the non-recombining electrons trajectories, already reported by Neyra and coworkers (Neyra E, et al 2018 J. Opt. 20, 034002). In order to build a real representation of the spatial dependence of the plasmonic-enhanced field in an analytic function, we fit the generated 'actual' field using two Gaussian functions. We have further analyzed and explored this plasmonic-modified ATI phenomenon in a model argon atom by using several driven wavelengths at intensities in the order of 1014 W cm-2. Throughout our contribution we carefully scrutinize the differences between the ATI obtained using spatially homogeneous and inhomogeneous laser fields. We present the various physical origins, or correspondingly distinct physical mechanisms, for the ATI generation driven by spatially bounded inhomogeneous fields.