Resonance-modulated wavelength scaling of high-order-harmonic generation from H2+

Wavelength scaling of high-order harmonic generation (HHG) in a non-Born-Oppenheimer treatment of ${\mathrm{H}}_{2}{}^{+}$ is investigated by numerical simulations of the time-dependent Schr\"odinger equation. The results show that the decrease in the wavelength-dependent HHG yield is reduced compared to that in the fixed-nucleus approximation. This slower wavelength scaling is related to the charge-resonance-enhanced ionization effect, which considerably increases the ionization rate at longer driving laser wavelengths due to the relatively larger nuclear separation. In addition, we find an oscillation structure in the wavelength scaling of HHG from ${\mathrm{H}}_{2}^{+}$. Upon decreasing the laser intensity or increasing the nuclear mass, the oscillation structure will shift towards a longer wavelength of the laser pulse. These results permit the generation of an efficient harmonic spectrum in the midinfrared regime by manipulating the nuclear dynamics of molecules.