Control high-order harmonic generation by molecular field-free alignment

The high-order harmonic generation (HHG) from aligned CO₂ molecules is investigated as a function of aligning laser intensity. Through controlling the molecular field-free alignment by varying the aligning laser intensity, the HHG process can be controlled. This phenomenon can be attributed to that the molecular HHG is dependent on the angle between the laser polarization and the internuclear axis, and the theoretical simulation is detailedly presented, which is consistent with the experimental result. This investigation is useful for the efficient harmonic generation from aligned molecules.