Scaling of Wave-Packet Dynamics in an Intense Midinfrared Field

A theoretical investigation is presented that examines the wavelength scaling from near-visible ($0.8text{ }text{ }ensuremath{mu}mathrm{m}$) to midinfrared ($2text{ }text{ }ensuremath{mu}mathrm{m}$) 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.