Molecules in intense laser fields: Beyond the dipole approximation

Abstract

The time-dependent Schrödinger equation is solved for a Born-Oppenheimer (static nuclei) three-dimensional $\mathrm{H}_2{}^{+}$ in super intense laser fields ($I=4\times {10}^{18}$, ${10}^{19}$, and $4\times {10}^{19}\mathrm{W}∕{\mathrm{cm}}^2$) at wavelength ${\lambda }_L=45\mathrm{nm}$ and $25\mathrm{nm}$ to assess the influence of nondipolar (magnetic) effects on high order harmonic generation spectra in molecules. It is found that even harmonics appear due to the magnetic field component direction perpendicular to the electric field polarization with intensities about two orders of magnitude less than the odd harmonics emitted along the electric field polarization. The even harmonics exhibit plateaus with cutoffs which exceed in intensity the odd harmonic plateaus and maximum energies predicted by semiclassical electron recollision models. Although the spectra are weak, the wavelength of the recollision electron in the maximum energy regions correspond to subatomic dimensions and the corresponding emitted photons have subnanometer wavelengths.