Scaling of Wave-Packet Dynamics in an Intense Midinfrared Field

A theoretical investigation is presented that examines the wavelength scaling from near-visible ($0.8\mu \mathrm{m}$) to midinfrared ($2\mu \mathrm{m}$) 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 Schrödinger equation (TDSE) in argon and the strong-field approximation in helium. The scaling of electron energies (${\lambda }^2$), harmonic cutoff (${\lambda }^2$), and attochirp (${\lambda }^{-1}$) agree with classical mechanics, but it is found that, surprisingly, the harmonic yield follows a ${\lambda }^{-(5–6)}$ scaling at constant intensity. In addition, the TDSE results reveal an unexpected contribution from higher-order returns of the rescattering electron wave packet.