Circularly polarized molecular high-order harmonic generation inH2+with intense laser pulses and static fields

Abstract

Molecular high-order harmonic generation (MHOHG) by a combined intense circularly polarized laser pulse and static electric field has been studied from the appropriate time-dependent Schr\"odinger equation (TDSE) for the ${{\mathrm{H}}_{2}}^{+}$ molecular ion. It is found that for a particular static field strength derived from a classical model, efficient MHOHG spectra are obtained with maximum energy ${I}_{p}$ $+$ 9.05${U}_{p}$, where ${I}_{p}$ is the ionization potential and ${U}_{p}={E}_{0}^{2}/4{m}_{e}{\ensuremath{\omega}}_{0}^{2}$ is the ponderomotive energy at amplitude ${E}_{0}$ and frequency ${\ensuremath{\omega}}_{0}$ of the circularly polarized laser pulse. The static field controls recollision of the electron with parent ions and is confirmed by numerical solutions of the ${{\mathrm{H}}_{2}}^{+}$ TDSE at equilibrium. To produce circularly polarized MHOHG spectra, a combination of an elliptically polarized pulse and a static electric field is found to be most efficient. A time-frequency analysis obtained via Gabor transforms is employed to identify electron recollision times responsible for the generation of these high-order harmonics. It is found that only single recollision trajectories contribute to the circularly polarized harmonics, thus generating new sources for high-frequency circularly polarized attosecond pulses.