Analysis of a higher-energy structure in nanotip enhanced fields

We investigate strong field ionization of an atomic gas in a plasmonically enhanced resulting from the illumination nanometer-sized structure with ultrafast laser pulse. use perturbation theory to derive approximate solution for electron's motion following ionization. These analytical estimates are corroborated by time-dependent Schrödinger equation and classical trajectory Monte Carlo simulations. Notably, our approach can be used obtain electron energy spectra without having rely on numerical This allows deeper study dependence spectrum properties near-field, suggesting electric sensor applications. expression location peak higher-energy (HES) as function parameters near-field decay length. find particularly frequency, lower frequencies causing significant upward shift final energies. Combined control width HES, which done changing size nanostructure, this points possibility using nanotips sources ultrashort beams tunable energy.