Analysis of recombination in high-order harmonic generation in molecules

We show that the dependence of high-order harmonic generation (HHG) on the molecular orientation can be understood within a theoretical treatment that does not involve the strong field of the laser. The results for ${\mathrm{H}}_{2}$ show excellent agreement with time-dependent strong-field calculations for model molecules, and this motivates a prediction for the orientation dependence of HHG from the ${\mathrm{N}}_{2}$ $3{\ensuremath{\sigma}}_{g}$ valence orbital. For both molecules, we find that the polarization of recombination photons is influenced by the molecular orientation. The variations are particularly pronounced for the ${\mathrm{N}}_{2}$ valence orbital, which can be explained by the presence of atomic $p$ orbitals.

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