Classical cutoff energies for electron emission and scattering at field-enhancing nanostructures with large ponderomotive amplitudes

Abstract

Electron rescattering using laser-enhancing nanostructures is a topic of particular interest for specialized high-brightness cathodes and attosecond high-harmonic generation. With ever-increasing ponderomotive amplitudes, the structure-induced longitudinal field profile is becoming more impactful on achievable energies. Using a classical approach, we investigate the limiting energies of electron emission and high-harmonic generation from nanostructures in the high-field regime. We perform generalized calculations for these cutoff energies for various structures by taking into account their particular spatial field profiles. We provide the peak electron emission and scattering energies as functions of the spatial adiabaticity parameter for decaying field profiles of the form r−1,r−2, and e−r/δ for nanoblades, nanotips, and plasmonics, respectively. These results are summarized in double-exponential fitted functions for ease of use. The maximal energies from each field profile differ by up to a factor of the ponderomotive energy. We also perform a simple near-field averaging analysis that produces satisfactorily accurate results. The introduction of a temporal Gaussian envelope decreases energies in most cases and modifies the ponderomotive force factor in a predictable manner. The effects of the carrier–envelope phase are exacerbated for few-cycle and shorter pulses.