CALCULATIONS OF MICROSCOPIC AND MACROSCOPIC PROPERTIES OF HIGH-HARMONIC GENERATION FROM MOLECULAR IONS

\begin{wrapfigure}{r}{0pt} \includegraphics[width=0.35\linewidth]{forwardDirection.eps} \caption{\small Calculated macrosopic high-harmonic signal in the forward direction. Mollow sidebands appear spaced by half the Rabi frequency to either side of the main harmonics.} \end{wrapfigure} High-harmonics generated in molecules can contain information about electronic structure and time-dependent dynamics induced by the driving laser. In molecular ions, it was recently predicted that the usual odd harmonics can be accompanied by sidebands at non-integer multiples of the fundamental frequency, analogous to the appearance of Mollow triplets in quantum optics [see figure]. These sidebands result from competition between two nonperturbative processes, Rabi oscillation and high-harmonic generation, and therefore offer additional insight into the dynamics of the molecule in a strong laser field. While the Mollow sideband effect shows up in theoretical calculations of single-molecule harmonic generation, in principle the macroscopic response must also be calculated to obtain a complete description. We evaluate the macroscopic harmonic spectrum by combining many single-molecule calculations at different intensities, obtained from time-dependent density functional theory calculations of $N_2^+$, and also from a 1D model potential. Our results suggest that the Mollow sidebands are approximately the same intensity as the main harmonics, and also they are radiated at wider angles, meaning they could be isolated more easily in an experiment. This work was supported by NSF JILA Physics Frontier Center (Grant No. PHY 1734006