Polarization of high-order harmonic generation in oriented molecules with intense ultrashort laser pulses

Using numerical solutions of the time-dependent Schr\"odinger equation we show that in oriented molecules one can control the polarization of molecular high-order harmonic generation (MHOHG) by intense linearly polarized pulses. For oriented triangular molecules, ${\mathrm{H}}_{3}{}^{+}/{\mathrm{H}}_{3}{}^{2+}$, one obtains even-order harmonics perpendicular to the laser polarization, whereas all odd-order harmonics have the same polarization as the laser polarization. For ${\mathrm{H}}_{2}{}^{+}/{\mathrm{H}}_{2}$ we show that only odd-order harmonics are generated for any orientation and their polarization is nearly parallel to the molecular axis. We describe these phenomena based on perturbation theory. Redshifts of the MHOHG spectra occur due to laser induced electron localization in non-Born-Oppenheimer dissociating molecules, reflecting the effect of nuclear dynamics. The numerical results illustrate the sensitivity of harmonic polarization to molecular geometry and nuclear dynamics.