Scaling of Wave-Packet Dynamics in an Intense Midinfrared Field

A theoretical investigation is presented that examines the wavelength scaling from near-visible ($0.8\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$) to midinfrared ($2\text{ }\text{ }\ensuremath{\mu}\mathrm{m}$) of the photoelectron distribution and high harmonics generated by a ``single'' atom in an intense electromagnetic field. The calculations use a numerical solution of the time-dependent Schr\"odinger equation (TDSE) in argon and the strong-field approximation in helium. The scaling of electron energies (${\ensuremath{\lambda}}^{2}$), harmonic cutoff (${\ensuremath{\lambda}}^{2}$), and attochirp (${\ensuremath{\lambda}}^{\ensuremath{-}1}$) agree with classical mechanics, but it is found that, surprisingly, the harmonic yield follows a ${\ensuremath{\lambda}}^{\ensuremath{-}(5--6)}$ scaling at constant intensity. In addition, the TDSE results reveal an unexpected contribution from higher-order returns of the rescattering electron wave packet.

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