Spatiotemporal evolution of ultrafast magnetic-field generation in molecules with intense bichromatic circularly polarized UV laser pulses

We present ultrafast magnetic-field pulse generation in aligned molecules from numerical solutions of time-dependent Schr\"odinger equations. The one-electron molecular ion ${{\mathrm{H}}_{2}}^{+}$ as a benchmark model is used to describe the ultrafast photophysics process. Schemes with bichromatic high-frequency corotating and counterrotating $(\ensuremath{\omega},2\ensuremath{\omega})$ and ($\ensuremath{\omega},3\ensuremath{\omega})$ circularly polarized UV laser pulses are presented to produce the spatial and temporal evolution of the generated magnetic field. We discuss how interference effects between multiple resonant excitations modulate the evolution of the generated magnetic field. It is found that the modulation of generated magnetic fields is dependent on the pulse frequency and helicity combination and the molecular alignment, which is attributed to the different resonant excitation processes with various molecular orbitals that vary the intramolecular coherent electron currents. The spatiotemporal evolution of generated magnetic fields is shown to be related and strongly different for molecular around-axis and in-plane electron currents. The scheme allows one to control the induced magnetic-field-pulse generation as a tool for ultrafast optical magnetism.