The previous results about the interference (or the laser intensity dependence) mainly focus on CO₂ and N₂ molecules, and there is a comparative lack of the investigation on O₂ molecule. Infrequently for O₂ molecule, Itatani et al. have showed that the high harmonics are enhanced when aligned near 45° with respect to the laser polarization due to the πg symmetry of its HOMO, and Vozzi et al. reported the order dependence of the harmonic yield due to the two-center interference. Researchers at State Key Laboratory of High Field Laser Physics——Shanghai Institute of Optics and Fines Mechanics (SIOM/China)  further measure the angular distribution and the laser intensity dependence of the harmonic yield from O₂ molecules. [OPTICS EXPRESS . Vol.19, No.1 ,2011;147-154].

In this work, researchers investigate the two-center interference in aligned O₂ molecules and perform a more comprehensive study of the interference characteristics by comparing with CO₂ molecules. Through the measurement of both the temporal evolution and the angular distribution of harmonic intensity, the detailed characteristics of intensity enhancement and suppression are observed, and the effects of the laser intensity and the two-centre interference are summarized. Moreover, the shift of the constructive spectral region in aligned O₂ molecules is demonstrated by tuning the driving laser intensity.