The role of the molecular alignment distribution with high harmonic generation (HHG) in aligned CO2 molecules is investigated and discussed in this letter. We first present the molecular field-free alignment and the polar plot of the weighted alignment distribution, and then also give the angular distribution of the molecular HHG. At last, we theoretically and experimentally demonstrate the alignment dependence for the molecular HHG. These results systematically verify the role of the molecular alignment distribution in the HHG process, which is useful for investigating the molecular dynamics in practical application.

A self-built broadband tunable infrared source is introduced here, and its notable merits are all-optical and high-conversion-efficiency. This infrared source contains an internal signal seed and two noncollinear optical parametric amplifiers. Based on this infrared source, we demonstrate the high harmonic generation from the different atomic and molecular gases using the different driving wavelengths. These results indicate that such system is ideally suited to be used as a tunable source for the laser processing and the physical science.

We investigate the angular distribution of high harmonic generation (HHG) from impulsively aligned CO2 molecules driving by the femtosecond laser. We first observe the HHG spectra under the different aligning angles and the different laser intensities. The angular distribution is found to be sensitive to both the harmonic order and the intensity of the driving laser pulse. At last, we theoretically and experimentally demonstrate the angular distribution with the different harmonic orders and the different laser intensities.

The alignment behaviors of polyatomic molecules under femtosecond laser pulses are experimentally and theoretically investigated. We observe the field-free alignment in C2H2 and CO2 molecules with High-Order Harmonic Generation (HHG) and discuss the evolution of the molecular rotational wave-packet with different laser parameters and ionization potentials. The results show that the molecular alignment degree depends not only on the laser parameters, but also on the molecular ionization potential. Finally we suggest the optimal aligning laser intensity to maximize the alignment degree for practical application.