Unraveling the dynamical origin of intense fifth harmonic generation from ${\mathrm{H}}_2^{+}$ in a linearly laser field

A systematic investigation of the fifth-harmonic generation in ${\mathrm{H}}_2^{+}$, driven in the vicinity of a five-photon resonance by a linearly polarized laser field, has been carried out by numerically solving the full three-dimensional time-dependent Schrödinger equation. We observe a pronounced enhancement of the fifth harmonic, while the intensities of the adjacent harmonics are significantly suppressed. Our analysis shows that such an enhancement of the fifth harmonic is mainly caused by the multiphoton resonance transition, as well as multichannel interference. In addition, we investigate the dependence of harmonic emission on laser intensity and molecular orientation to identify the optimal conditions for enhancing the fifth-harmonic generation. Our results provide useful insights for producing coherent ultraviolet radiation at 106 nm experimentally.